ci: add rust-cache action after toolchain install

Author: Firestar99

.github/workflows/ci.yaml

@@ -41,6 +41,11 @@ jobs:
       # figure out native target triple while we're at it
       - name: install rust-toolchain
         run: echo "TARGET=$(rustc --print host-tuple)" >> "$GITHUB_ENV"
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: |
+            .
+            tests/difftests/tests
       # Fetch dependencies in a separate step to clearly show how long each part
       # of the testing takes
       - name: cargo fetch --locked
@@ -94,6 +99,11 @@ jobs:
           stripdown: true
       - name: install rust-toolchain
         run: cargo version
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: |
+            .
+            tests/difftests/tests
       - name: cargo fetch --locked
         run: cargo fetch --locked --target ${{ matrix.target }}
 
@@ -138,6 +148,11 @@ jobs:
           stripdown: true
       - name: install rust-toolchain
         run: echo "TARGET=$(rustc --print host-tuple)" >> "$GITHUB_ENV"
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: |
+            .
+            tests/difftests/tests
       - name: cargo fetch --locked
         run: cargo fetch --locked --target $TARGET
       - name: compiletest
@@ -173,6 +188,11 @@ jobs:
           sudo apt install -y xvfb libgl1-mesa-dri libxcb-xfixes0-dev mesa-vulkan-drivers
       - name: install rust-toolchain
         run: echo "TARGET=$(rustc --print host-tuple)" >> "$GITHUB_ENV"
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: |
+            .
+            tests/difftests/tests
       - name: cargo fetch --locked
         run: cargo fetch --locked --target $TARGET
       - name: cargo fetch --locked difftests
@@ -220,6 +240,11 @@ jobs:
       # cargo version is a random command that forces the installation of rust-toolchain
       - name: install rust-toolchain
         run: cargo version
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: |
+            .
+            tests/difftests/tests
       - name: Install rustup components
         run: rustup component add rustfmt clippy
       - name: cargo fetch --locked