Bump version to 0.27.0

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.58%. Comparing base (2a66a0d) to head (534ab71). Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3111 +/- ## ========================================== - Coverage 99.58% 99.58% -0.01% ========================================== Files 121 121 Lines 18166 18157 -9 Branches 3275 3272 -3 ========================================== - Hits 18091 18082 -9 Misses 52 52 Partials 23 23 ``` | [Files with missing lines](https://app.codecov.io/gh/python-trio/trio/pull/3111?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=python-trio) | Coverage Δ | | |---|---|---| | [src/trio/\_tests/test\_testing\_raisesgroup.py](https://app.codecov.io/gh/python-trio/trio/pull/3111?src=pr&el=tree&filepath=src%2Ftrio%2F_tests%2Ftest_testing_raisesgroup.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=python-trio#diff-c3JjL3RyaW8vX3Rlc3RzL3Rlc3RfdGVzdGluZ19yYWlzZXNncm91cC5weQ==) | `100.00% <ø> (ø)` | | | [src/trio/\_version.py](https://app.codecov.io/gh/python-trio/trio/pull/3111?src=pr&el=tree&filepath=src%2Ftrio%2F_version.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=python-trio#diff-c3JjL3RyaW8vX3ZlcnNpb24ucHk=) | `100.00% <100.00%> (ø)` | | | [src/trio/testing/\_raises\_group.py](https://app.codecov.io/gh/python-trio/trio/pull/3111?src=pr&el=tree&filepath=src%2Ftrio%2Ftesting%2F_raises_group.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=python-trio#diff-c3JjL3RyaW8vdGVzdGluZy9fcmFpc2VzX2dyb3VwLnB5) | `100.00% <ø> (ø)` | |