Swift: simplify codeql workflow

* remove ql test running and upgrade/downgrade scripts checking (now
  done internally)
* removed all the bazel caching stuff, that never really worked any way
* moved `misc/codegen` generic testing to a separate workflow, as it's
  not swift specific any more
* reinstanted checking that the extractor can be built locally from
  the `codeql` repo.

.github/workflows/codegen.yml

@@ -0,0 +1,34 @@
+name: Codegen
+
+on:
+  pull_request:
+    paths:
+      - "misc/bazel/**"
+      - "misc/codegen/**"
+      - "*.bazel*"
+      - .github/workflows/codegen.yml
+      - .pre-commit-config.yaml
+    branches:
+      - main
+      - rc/*
+      - codeql-cli-*
+
+permissions:
+  contents: read
+
+jobs:
+  codegen:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v4
+        with:
+          python-version-file: 'misc/codegen/.python-version'
+      - uses: pre-commit/action@646c83fcd040023954eafda54b4db0192ce70507
+        name: Check that python code is properly formatted
+        with:
+          extra_args: autopep8 --all-files
+      - name: Run codegen tests
+        shell: bash
+        run: |
+          bazel test //misc/codegen/...