ci: fix runner.os -> matrix.os

Author: teo-lohrer-su

.github/workflows/rust.yaml

@@ -31,9 +31,9 @@ jobs:
           path: |
             ~/.cargo/registry
             ~/.cargo/git
-          key: ${{ runner.os }}-cargo-${{ matrix.rust }}-${{ hashFiles('**/Cargo.lock') }}
+          key: ${{ matrix.os }}-cargo-${{ matrix.rust }}-${{ hashFiles('**/Cargo.lock') }}
           restore-keys: |
-            ${{ runner.os }}-cargo-${{ matrix.rust }}-
+            ${{ matrix.os }}-cargo-${{ matrix.rust }}-
 
       - name: Set up Rust
         uses: actions-rs/toolchain@v1