WIP. Attempt to fix GH Actions with better caching

My hunch is that the Ubuntu 24.04 and Ubuntu 22.04 caches are getting
co-mingled. Let’s find out.

Author: onethumb

.github/workflows/tests.yml

@@ -22,12 +22,11 @@ jobs:
         with:
           toolchain: ${{ matrix.rust-toolchain }}
           components: rustfmt, clippy
+          cache-key: ${{ matrix.os }}-${{ matrix.rust-toolchain }}
       - name: Check
         run: cargo check
       - name: Architecture check
         run: cargo run arch-check
-      - name: Architecture check (Optimized)
-        run: cargo run arch-check
       - if: ${{ matrix.rust-toolchain != 'nightly' }}
         name: Format
         run: cargo fmt -- --check