ci: bump apify/actions/pnpm-install to v1.3.1

[vdusek]

Bumps the pinned apify/actions/pnpm-install composite action to v1.3.1.

That release updates actions/cache to v6.1.0, so the action runs on the Node.js 24 runtime. It clears the "Node.js 20 is deprecated" warning that shows up on every CI run. For details, see apify/actions#29.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.33%. Comparing base (ccfff76) to head (52567f3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2002      +/-   ##
==========================================
- Coverage   93.35%   93.33%   -0.02%     
==========================================
  Files         179      179              
  Lines       12482    12482              
==========================================
- Hits        11652    11650       -2     
- Misses        830      832       +2     

Flag	Coverage Δ
unit	93.33% <ø> (-0.02%)	⬇️

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