Replace type checks with isinstance

[bencomp]

This should remove all Flake8 E721 errors that cause build failures.

[codecov[bot]]

Codecov Report

Patch coverage: 82.35% and no project coverage change.

Comparison is base (6c84cfb) 58.35% compared to head (1af1767) 58.35%. Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #427 +/- ## ======================================= Coverage 58.35% 58.35% ======================================= Files 10 10 Lines 1340 1340 ======================================= Hits 782 782 Misses 558 558 ``` | [Files Changed](https://app.codecov.io/gh/domainaware/parsedmarc/pull/427?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=domainaware) | Coverage Δ | | |---|---|---| | [parsedmarc/\_\_init\_\_.py](https://app.codecov.io/gh/domainaware/parsedmarc/pull/427?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=domainaware#diff-cGFyc2VkbWFyYy9fX2luaXRfXy5weQ==) | `61.73% <80.00%> (ø)` | | | [parsedmarc/utils.py](https://app.codecov.io/gh/domainaware/parsedmarc/pull/427?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=domainaware#diff-cGFyc2VkbWFyYy91dGlscy5weQ==) | `69.35% <100.00%> (ø)` | |

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[AnaelMobilia]

Dear @bencomp ,

It looks like @seanthegeek make some flake8 E721 issues. I suggest to rebase your PR on current main.

Bests regards,

[seanthegeek]

I already did this. Thanks.