Bump deprecated GitHub Actions to current major versions

[Valyrian-Code]

Bumps GitHub Actions in the flake8 (Code formatting) and codeql (CodeQL) workflows from deprecated major versions to the current ones. No behaviour change.

• actions/checkout@v3 → @v6 (matches the versions already used in tests.yml / run-test-suite.yml)
• actions/setup-python@v2 → @v6
• github/codeql-action/{init,autobuild,analyze}@v2 → @v3

Rationale: actions/checkout@v3 and actions/setup-python@v2 run on the end-of-life Node 16 runner, and github/codeql-action@v2 has been deprecated by GitHub. These emit deprecation warnings today and will eventually stop executing.

Checklist

For all pull requests:

• Confirm you have read the contribution guidelines
• You have sent a Contribution Licence Agreement (CLA) as necessary — CI-only change, no source or new files (small-change exemption)
• Make sure the first PR targets the master branch

For core and extension modules:

• There is a ticket describing the issue — CI maintenance, not visible to end users (template exemption for "changes not visible to end-users")
• The issue connected to the PR must have Labels and Milestone assigned — N/A (no issue, per the exemption above)
• PR for bug fixes and small new features are presented as a single commit
• PR title must be in the form "[Fixes #<issue_number>] Title of the PR" — N/A (no issue, per the exemption above)
• New unit tests have been added — N/A: this is a CI configuration change with no runtime code; correctness is exercised by this PR's own workflow runs

[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have the users @Valyrian-Code on file. In order for us to review and merge your code, please contact the project maintainers to get yourself added.

[Copilot]

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[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[Valyrian-Code]

Signed CLA emailed to info@osgeo.org as @Valyrian-Code. Could a maintainer add me to the .clabot allowlist? This is a small CI-only change. Thanks!