code block renders differently after formatting

[jnnnnn]

Describe the problem

The following markdown triggers an error about rendering differently in version 1.1.0 on Windows:

```~/.gitconfig
[user]

I know this is pretty weird markdown (I wrote it by mistake), 
but it was buried in a 20,000 line file and prevents the entire file from being formatted.

### Link to your repository or website

_No response_

### Steps to reproduce

Save the above code block in a file and run mdformat on it. 

### The version of Python you're using

3.9.5

### Your operating system

Windows 10

### Versions of your packages

alabaster==0.7.12
anyio==3.3.0
appdirs==1.4.4
argon2-cffi==20.1.0
arrow==1.0.3
attrs==20.3.0
autopep8==1.5.7
Babel==2.9.1
backcall==0.2.0
beautifulsoup4==4.9.3
binaryornot==0.4.4
bitarray==2.3.4
black==20.8b1
bleach==4.1.0
bottle==0.12.19
bs4==0.0.1
cachetools==4.2.1
certifi==2020.12.5
cffi==1.14.5
chardet==3.0.4
click==7.1.2
colorama==0.4.4
conan==1.28.2
conan-package-tools==0.34.4
cookiecutter==1.7.3
cryptography==3.4.7
datadog==0.41.0
debugpy==1.4.1
decorator==4.4.2
defusedxml==0.7.1
Deprecated==1.2.12
deprecation==2.0.7
distro==1.1.0
docutils==0.16
entrypoints==0.3
fasteners==0.16
future==0.18.2
gitdb==4.0.7
GitPython==3.1.14
google-api-core==1.26.3
google-api-python-client==2.1.0
google-auth==1.28.0
google-auth-httplib2==0.1.0
google-auth-oauthlib==0.4.4
googleapis-common-protos==1.53.0
greenlet==1.1.1
grpcio==1.37.0
grpcio-tools==1.37.0
httplib2==0.19.1
idna==2.10
imagesize==1.2.0
importlib-metadata==4.7.1
ipykernel==6.2.0
ipython==7.29.0
ipython-genutils==0.2.0
ipywidgets==7.6.3
iress-ci-utils==0.72.0
iress-conan-utils==5.64.0
iress-package-tools==1.2.23
iress-sdo-cpp==3.1.333.0
javaproperties==0.8.0
jedi==0.18.0
Jinja2==2.11.3
jinja2-time==0.2.0
json5==0.9.6
jsonschema==3.2.0
jupyter-book==0.11.3
jupyter-cache==0.4.3
jupyter-client==7.0.1
jupyter-core==4.7.1
jupyter-server==1.10.2
jupyter-server-mathjax==0.2.3
jupyter-sphinx==0.3.2
jupyterlab-widgets==1.0.0
jupytext==1.10.3
latexcodec==2.0.1
linkify-it-py==1.0.1
lxml==4.6.4
markdown-it-py==1.1.0
MarkupSafe==1.1.1
matplotlib-inline==0.1.2
mdformat==0.7.10
mdit-py-plugins==0.2.6
mercurial==5.9.1
mistune==0.8.4
msedge-selenium-tools==3.141.3
mypy-extensions==0.4.3
myst-nb==0.12.3
myst-parser==0.13.7
nbclient==0.5.4
nbconvert==5.6.1
nbdime==3.1.0
nbformat==5.1.3
nest-asyncio==1.5.1
networkx==2.5.1
node-semver==0.6.1
notebook==6.4.3
numpy==1.21.4
oauth2client==4.1.3
oauthlib==3.1.0
packaging==20.9
pandocfilters==1.4.3
parso==0.8.2
patch-ng==1.17.4
pathspec==0.8.1
pefile==2019.4.18
-e git+https://github.com/alex-nitrokey/python-pgpdump@196f48e7a48cff9d7ade2d7c32bf6186b5a6fc34#egg=pgpdump3
pickleshare==0.7.5
pluginbase==1.0.0
poyo==0.5.0
prometheus-client==0.11.0
prompt-toolkit==3.0.18
protobuf==3.15.7
psutil==5.8.0
pyasn1==0.4.8
pyasn1-modules==0.2.8
pybtex==0.24.0
pybtex-docutils==1.0.1
pycodestyle==2.7.0
pycparser==2.20
pycryptodome==3.11.0
pydata-sphinx-theme==0.6.3
pydot==1.4.2
pyftpdlib==1.5.6
PyGithub==1.54.0.1
Pygments==2.8.1
PyIressTest==21.11.905
PyJWT==1.7.1
pyodbc==4.0.30
pyparsing==2.4.7
pyrsistent==0.18.0
python-dateutil==2.8.2
python-slugify==5.0.2
pytz==2021.3
pywin32==301
pywinpty==1.1.3
PyYAML==5.4.1
pyzmq==22.2.1
quick-jira==0.1.6
regex==2021.4.4
requests==2.24.0
requests-oauthlib==1.3.0
requests-unixsocket==0.2.0
rsa==4.7.2
selenium==3.141.0
Send2Trash==1.8.0
six==1.14.0
smmap==4.0.0
sniffio==1.2.0
snowballstemmer==2.1.0
soupsieve==2.2.1
Sphinx==3.5.4
sphinx-book-theme==0.1.3
sphinx-comments==0.0.3
sphinx-copybutton==0.4.0
sphinx-external-toc==0.2.3
sphinx-jupyterbook-latex==0.4.2
sphinx-multitoc-numbering==0.1.3
sphinx-panels==0.5.2
sphinx-thebe==0.0.10
sphinx-togglebutton==0.2.3
sphinxcontrib-applehelp==1.0.2
sphinxcontrib-bibtex==2.2.1
sphinxcontrib-devhelp==1.0.2
sphinxcontrib-htmlhelp==2.0.0
sphinxcontrib-jsmath==1.0.1
sphinxcontrib-qthelp==1.0.3
sphinxcontrib-serializinghtml==1.1.5
SQLAlchemy==1.4.23
suds-ijurko==0.601
tabulate==0.8.9
tempdir-ro==0.1.6
terminado==0.11.1
testpath==0.5.0
text-unidecode==1.3
toml==0.10.2
tomli==1.2.2
tornado==6.1
tqdm==4.60.0
traitlets==5.0.5
typed-ast==1.4.3
typing-extensions==3.7.4.3
uc-micro-py==1.0.1
uritemplate==3.0.1
urllib3==1.25.11
wcwidth==0.2.5
wealthti-protos==2.2.0
webencodings==0.5.1
websocket-client==1.2.1
websockets==8.1
widgetsnbextension==3.5.1
wrapt==1.12.1
xkcdpass==1.17.6
zipp==3.5.0

### Additional context

_No response_

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[hukkin]

Thanks for the issue!

Can confirm this is a bug. The fix is here https://github.com/executablebooks/mdformat/pull/282 and will be included in the next release.