chore(ci): harden workflows, pin actions, add zizmor + dependabot

[banesullivan]

Part of a org-wide CI/security sweep, following pyOpenSci/metrics#171

Changes

Workflows (add-help-wanted, publish-pypi, run-script, run-tests, test-run-script, test-update-contribs):

• Pinned every action to a commit SHA with a # vX.Y.Z comment
• Added missing permissions blocks (least-privilege) and name: fields
• Added concurrency so superseded runs cancel
• Corrected stale action SHAs

New zizmor.yml workflow runs zizmor on workflow changes and uploads SARIF to code scanning.

Repo config:

• dependabot.yml: weekly cadence, added the pip ecosystem (was actions-only)
• .github/zizmor.yml: 4 allow-list entries, each with a justification comment
• .pre-commit-config.yaml: woodruffw/zizmor-pre-commit to zizmorcore/zizmor-pre-commit v1.24.1 (repo was renamed)

follow-ups

• GHPROJECT_HELP_WANTED: the org-level token cannot move to a deployment environment without breaking the issues: labeled trigger (noted in the allow-list).
• Verify PYOS_PR_TOKEN and CODECOV_TOKEN exist at repo level.

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.06%. Comparing base (ce29a09) to head (d3eba15).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #363   +/-   ##
=======================================
  Coverage   79.06%   79.06%           
=======================================
  Files          12       12           
  Lines         812      812           
  Branches      108      108           
=======================================
  Hits          642      642           
  Misses        155      155           
  Partials       15       15           

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