Don't share target-cpu=native cache between github runners with different hardware

Author: HadrienG2

.github/workflows/ci.yml

@@ -302,10 +302,22 @@ jobs:
       - name: Checkout sources
         uses: actions/checkout@v4
 
+      # Cargo doesn't know when to rebuild a target-cpu=native cache when it's
+      # migrated across machines, so a CI node must not be exposed to the target
+      # directory generated by another CI node in target-cpu=native mode.
+      - name: Avoid abusive caching with target-cpu=native
+        run: |
+            if [[ ${RUSTFLAGS} =~ '-C target-cpu=native' ]]; then
+                cp /proc/cpuinfo cpuinfo.key
+            else
+                echo "Generic x86_64" >cpuinfo.key
+            fi
+
       - name: Set up toolchain
         uses: actions-rust-lang/setup-rust-toolchain@v1
         with:
           toolchain: ${{ matrix.toolchain }}
+          cache-key: ${{ hashFiles(cpuinfo.key) }}
 
       - name: Run tests
         run: cargo test --workspace ${{ matrix.cargo-flags }}