Bump Swatinem/rust-cache from 2.5.0 to 2.6.0 (#2968)

Bumps [Swatinem/rust-cache](https://github.com/swatinem/rust-cache) from 2.5.0 to 2.6.0.
- [Release notes](https://github.com/swatinem/rust-cache/releases)
- [Changelog](https://github.com/Swatinem/rust-cache/blob/master/CHANGELOG.md)
- [Commits](https://github.com/swatinem/rust-cache/compare/2656b87321093db1cb55fbd73183d195214fdfd1...b8a6852b4f997182bdea832df3f9e153038b5191)

---
updated-dependencies:
- dependency-name: Swatinem/rust-cache
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

cumulus/.github/workflows/docs.yml

@@ -23,7 +23,7 @@ jobs:
         run:  rustup show
 
       - name: Rust cache
-        uses: Swatinem/rust-cache@2656b87321093db1cb55fbd73183d195214fdfd1 # v2.5.0
+        uses: Swatinem/rust-cache@b8a6852b4f997182bdea832df3f9e153038b5191 # v2.6.0
 
       - name: Build rustdocs
         run:  SKIP_WASM_BUILD=1 cargo doc --all --no-deps