ci: always run Tests workflow and gate jobs on changed paths

[itssimon]

Summary

Requiring ci-gate in branch protection broke PRs whose changes don't match the Tests workflow's paths: filters (e.g. some renovate PRs): the workflow never triggers, so the required ci-gate check never appears and the PR is stuck. This removes the trigger-level paths: filters so the workflow always runs, and moves change detection into a changes job (dorny/paths-filter) that gates the check and test jobs individually. When nothing relevant changed, those jobs are skipped and ci-gate still reports success, so the required check always resolves. Same pattern as the Check workflow in apitally/cloud.

Validation

This PR only touches the workflow file, which is itself in the filter, so check and test run here; the skipped-jobs path is exercised by PRs that don't touch the filtered paths once merged.

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Summary by cubic

Always run the Tests workflow so the required ci-gate check always appears. Gate check and test on changed paths so irrelevant PRs skip work but still pass ci-gate.

• Bug Fixes
  • Removed trigger-level paths filters so the workflow always starts.
  • Added a changes job using dorny/paths-filter to detect relevant file changes.
  • Run check and test only when changes match (or on workflow_dispatch); ci-gate depends on them and reports success even when they’re skipped.

^{Written for commit ad197d2. Summary will update on new commits.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.25%. Comparing base (dbe4ca2) to head (ad197d2).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #52   +/-   ##
=======================================
  Coverage   91.25%   91.25%           
=======================================
  Files          12       12           
  Lines        2070     2070           
=======================================
  Hits         1889     1889           
  Misses        181      181           

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