Update Swatinem/rust-cache action to v2.8.1

Author: oxide-renovate[bot]

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@stable
         with:
           components: rustfmt, clippy
-      - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6 # v2.7.8
+      - uses: Swatinem/rust-cache@f13886b937689c021905a6b90929199931d60db1 # v2.8.1
       - uses: taiki-e/install-action@just
       - uses: taiki-e/install-action@cargo-hack
       - name: Lint (clippy)