ci: unpin mypy from lint job

Author: dcbaker

.github/workflows/lint.yml

@@ -52,8 +52,7 @@ jobs:
     - uses: actions/setup-python@v5
       with:
         python-version: '3.x'
-    # Pin mypy to version 1.8, so we retain the ability to lint for Python 3.7
-    - run: python -m pip install "mypy==1.8" strictyaml truststore types-PyYAML types-tqdm types-chevron
+    - run: python -m pip install strictyaml truststore types-PyYAML types-tqdm types-chevron
     - run: python run_mypy.py --allver
       env:
         PYTHONUNBUFFERED: 1