Tighten up CI with Zizmor

[akx]

Run uvx zizmor .github/workflows/ and heed its complaints:

• Pin third-party actions
• Adjust certain permissions

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.93%. Comparing base (3bcc34e) to head (1a181e7).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1230   +/-   ##
=======================================
  Coverage   91.93%   91.93%           
=======================================
  Files          27       27           
  Lines        4688     4688           
=======================================
  Hits         4310     4310           
  Misses        378      378           

Flag	Coverage Δ
macos-14-3.10	90.97% <ø> (ø)
macos-14-3.11	90.91% <ø> (ø)
macos-14-3.12	91.12% <ø> (ø)
macos-14-3.13	91.12% <ø> (ø)
macos-14-3.14	91.10% <ø> (ø)
macos-14-3.8	90.84% <ø> (ø)
macos-14-3.9	90.90% <ø> (ø)
macos-14-pypy3.10	90.97% <ø> (ø)
ubuntu-24.04-3.10	90.99% <ø> (ø)
ubuntu-24.04-3.11	90.93% <ø> (ø)
ubuntu-24.04-3.12	91.14% <ø> (ø)
ubuntu-24.04-3.13	91.14% <ø> (ø)
ubuntu-24.04-3.14	91.12% <ø> (ø)
ubuntu-24.04-3.8	90.86% <ø> (ø)
ubuntu-24.04-3.9	90.92% <ø> (ø)
ubuntu-24.04-pypy3.10	90.99% <ø> (ø)
windows-2022-3.10	90.98% <ø> (ø)
windows-2022-3.11	90.92% <ø> (ø)
windows-2022-3.12	91.13% <ø> (ø)
windows-2022-3.13	91.13% <ø> (ø)
windows-2022-3.14	91.11% <ø> (ø)
windows-2022-3.8	90.96% <ø> (ø)
windows-2022-3.9	90.91% <ø> (ø)
windows-2022-pypy3.10	90.98% <ø> (ø)

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