ci: cache per rust version

Author: phip1611

.github/workflows/_build-rust.yml

@@ -52,8 +52,8 @@ jobs:
             ~/.cargo/registry/cache/
             ~/.cargo/git/db/
             target/
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
-          restore-keys: ${{ runner.os }}-cargo-
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}-${{ inputs.rust-version }}
+          restore-keys: ${{ runner.os }}-cargo-${{ inputs.rust-version }}
       - run: cargo version
       - name: Code Formatting
         if: ${{ inputs.do-style-check }}