Fix: [CI] unbreak Linux releases by using a slightly older rust-cache action

The maintainer bumped node16 -> node20 in a patch version, which
is a bit awkward for us, as we can't run node20 in this workflow
(yet). Most other actions used a major version for that, and for
similar reasons we cannot upgrade "download-artifact" to v4.

This is a temporary solution, while we start looking into how to
support node20 in this workflow.

.github/workflows/release-linux.yml

@@ -50,7 +50,7 @@ jobs:
       uses: dtolnay/rust-toolchain@stable
 
     - name: Enable Rust cache
-      uses: Swatinem/rust-cache@v2
+      uses: Swatinem/rust-cache@v2.7.0
 
     - name: Setup vcpkg caching
       uses: actions/github-script@v6