Remove last use of installPython

- Add explicit `setup-python` step with condition to the workflow that was still using it
- This allows simplifying the logic in `sync.ts`

Author: mbg

.github/workflows/__multi-language-autodetect.yml

@@ -4,9 +4,16 @@ operatingSystems: ["macos", "ubuntu"]
 env:
   CODEQL_ACTION_RESOLVE_SUPPORTED_LANGUAGES_USING_CLI: true
 installGo: true
-installPython: true
 installDotNet: true
 steps:
+  - name: Install Python 3.13 for older CLI versions
+    # We need Python 3.13 for older CLI versions because they are not compatible with Python 3.14 or newer.
+    # See https://github.com/github/codeql-action/pull/3212
+    if: matrix.version != 'nightly-latest' && matrix.version != 'linked'
+    uses: actions/setup-python@v6
+    with:
+      python-version: "3.13"
+
   - name: Use Xcode 16
     if: runner.os == 'macOS' && matrix.version != 'nightly-latest'
     run: sudo xcode-select -s "/Applications/Xcode_16.app"