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 94.52%. Comparing base (7a5b157) to head (644b8e7).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #913      +/-   ##
==========================================
- Coverage   94.54%   94.52%   -0.02%     
==========================================
  Files          48       48              
  Lines        5098     5098              
==========================================
- Hits         4820     4819       -1     
- Misses        278      279       +1     

Flag	Coverage Δ
integration	92.62% <ø> (-0.28%)	⬇️
unit	83.36% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.