Bump actions/cache from 3 to 4 (#198)

Bumps [actions/cache](https://github.com/actions/cache) from 3 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v3...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -81,7 +81,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - name: Use cached cargo-readme
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         id: cargo-readme-cache
         with:
           path: ~/.cargo/bin/cargo-readme