Don't specify a subdir in mypy CI cli (#9416)

* Don't specify a subdir in mypy CI cli

We should test that a simple `mypy` invocation works, because that's what's expected to run locally, and instead move any arguments to config files

(I hit this because I'm getting type errors locally, though this doesn't fix them, it eliminates a source of difference)

Author: max-sixty

.github/workflows/ci-additional.yaml

@@ -127,7 +127,7 @@ jobs:
 
       - name: Run mypy
         run: |
-          python -m mypy --install-types --non-interactive --cobertura-xml-report mypy_report xarray/
+          python -m mypy --install-types --non-interactive --cobertura-xml-report mypy_report
 
       - name: Upload mypy coverage to Codecov
         uses: codecov/codecov-action@v4.5.0
@@ -138,7 +138,7 @@ jobs:
           name: codecov-umbrella
           fail_ci_if_error: false
 
-  mypy39:
+  mypy-min:
     name: Mypy 3.10
     runs-on: "ubuntu-latest"
     needs: detect-ci-trigger
@@ -181,7 +181,7 @@ jobs:
 
       - name: Run mypy
         run: |
-          python -m mypy --install-types --non-interactive --cobertura-xml-report mypy_report xarray/
+          python -m mypy --install-types --non-interactive --cobertura-xml-report mypy_report
 
       - name: Upload mypy coverage to Codecov
         uses: codecov/codecov-action@v4.5.0