ci: update toolchains and let renovate update action inputs (#40092)

- Let renovate update hyphenated action inputs like `python-version`
- Python 3.14 → 3.15 in CI
- Download gh 2.103.2 directly in the release workflow instead of using
`install-gh-cli-action` with 2.39.1
- Devcontainer Go image 1.26 → 1.27
- Snap build toolchains Go 1.26 → 1.27 and Node 24 → 26

.github/actions/python-setup/action.yml

@@ -6,5 +6,5 @@ runs:
   steps:
     - uses: astral-sh/setup-uv@1c37ad07a6a961277cf70c0d37d6f313000f5884 # v10.3.0
       with:
-        python-version: 3.14
+        python-version: 3.15 # renovate: datasource=python-version depName=python versioning=python
         save-cache: ${{ github.workflow == 'cache-seeder' }}