CI: Fix Octave installation on MacOS

[blink1073]

Description

The test-other-systems macOS job restores a cached Homebrew Octave Cellar archive (key macos-brew-octave-11.3.0-image-) to skip rebuilding Octave on every run. That cache does not pin to a specific runner image version, so when GitHub bumps the bundled gcc version in the macos-15-arm64 runner image, the restored Octave binaries (linked against the old gcc's libgfortran.5.dylib via the current symlink) no longer resolve, and octave --version aborts with a dyld load failure.

Changes

• After restoring the cached Octave Cellar, run brew reinstall octave so Octave is rebuilt/relinked against whichever gcc is actually present on the runner image, instead of trusting a stale cached binary's dependency links.
• This trades a bit of cache effectiveness for correctness: the cache still saves the Octave download/build time when the toolchain hasn't moved, but brew reinstall self-heals the install whenever it has.

Backwards-incompatible changes

None

Testing

CI — verified the test-other-systems (macos-latest) job runs octave --version and available_graphics_toolkits successfully after cache restore + reinstall.

AI usage

• Some or all of the content of this PR was generated by AI.
• The human author has carefully reviewed this PR and run this code.
• AI tools and models used: None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.90%. Comparing base (37ee303) to head (1a50bdc).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #346   +/-   ##
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  Coverage   92.90%   92.90%           
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  Files           6        6           
  Lines         437      437           
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  Hits          406      406           
  Misses         31       31           

Flag	Coverage Δ
linux	92.67% <ø> (ø)
windows	92.90% <ø> (ø)

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