Add basic mypy workflow to CI

.github/workflows/mypy-clinic.yml

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+name: Run mypy on Tools/clinic
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    paths:
+      - "Tools/clinic/**/*"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  mypy:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v4
+        with:
+          python-version: "3.11"
+          cache: pip
+          cache-dependency-path: .github/workflows/mypy-clinic.yml
+      - run: pip install mypy==1.3.0
+      - run: mypy --config-file Tools/clinic/mypy.ini

Tools/clinic/mypy.ini

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+[mypy]
+pretty = True
+enable_error_code = ignore-without-code
+disallow_any_generics = True
+strict_concatenate = True
+warn_redundant_casts = True
+warn_unused_ignores = True
+warn_unused_configs = True
+files = Tools/clinic/