bump @actions/cache to 4.0.3 to fix caching

[dawedawe]

This should fix #102
See here for the failing caching before and the working caching after
Before:
https://github.com/dawedawe/tusistor/actions/runs/15087191049/job/42411230897#step:3:75

Saving rustdoc cache using key semver-semver-checks-30fd6267800aa10d-linux-rustc-1.87.0-(17067e9ac-2025-05-09)-cargo-semver-checks-0.41.0-94bdc12f5421663f347940d3ca9831ea-semver-checks-rustdoc-2db6c6f3568e6a7322bcd9d1bf0314e0057bc77b
/usr/bin/tar --posix -cf cache.tzst --exclude cache.tzst -P -C /home/runner/work/tusistor/tusistor --files-from manifest.txt --use-compress-program zstdmt
Failed to save: Unable to reserve cache with key semver-semver-checks-30fd6267800aa10d-linux-rustc-1.87.0-(17067e9ac-2025-05-09)-cargo-semver-checks-0.41.0-94bdc12f5421663f347940d3ca9831ea-semver-checks-rustdoc-2db6c6f3568e6a7322bcd9d1bf0314e0057bc77b, another job may be creating this cache. More details: This legacy service is shutting down, effective April 15, 2025. Migrate to the new service ASAP. For more information: https://gh.io/gha-cache-sunset

After:
https://github.com/dawedawe/tusistor/actions/runs/15087242363/job/42411341332#step:3:74

Saving rustdoc cache using key semver-semver-checks-30fd6267800aa10d-linux-rustc-1.87.0-(17067e9ac-2025-05-09)-cargo-semver-checks-0.41.0-94bdc12f5421663f347940d3ca9831ea-semver-checks-rustdoc-2db6c6f3568e6a7322bcd9d1bf0314e0057bc77b
/usr/bin/tar --posix -cf cache.tzst --exclude cache.tzst -P -C /home/runner/work/tusistor/tusistor --files-from manifest.txt --use-compress-program zstdmt
Sent 44385 of 44385 (100.0%), 0.2 MBs/sec

[obi1kenobi]

Thanks for the PR, much appreciated! Our CI is in a bit of a sad state, so I might merge the main branch into your PR's branch a few times to try to get everything else to pass.