.github: Cache builds in CI

Author: simnalamburt

.github/workflows/ci.yml

@@ -2,12 +2,14 @@ on: [push, pull_request]
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
     strategy:
       matrix:
         glium: ["", "glium-support"]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
       - run: cargo build --features '${{ matrix.glium }}'
       - run: cargo test --features '${{ matrix.glium }}'
       - run: cargo clippy --features '${{ matrix.glium }}' --no-deps -- -D warnings