ci: reuse compiled integration tests and prebuilt images

Updates #3542

(cherry picked from commit c9852c43da)

.github/workflows/test-integration.yaml

@@ -43,15 +43,13 @@ jobs:
         with:
           primary-key: nix-${{ runner.os }}-${{ runner.arch }}-${{ hashFiles('**/*.nix', '**/flake.lock') }}
           restore-prefixes-first-match: nix-${{ runner.os }}-${{ runner.arch }}
-      - name: Build binaries and warm Go cache
+      - name: Build binaries
         if: steps.changed-files.outputs.files == 'true'
         run: |
-          # Build all Go binaries in one nix shell to maximize cache reuse
           nix develop --command -- bash -c '
             go build -o hi ./cmd/hi
             CGO_ENABLED=0 GOOS=linux go build -o headscale ./cmd/headscale
-            # Build integration test binary to warm the cache with all dependencies
-            go test -c ./integration -o /dev/null 2>/dev/null || true
+            CGO_ENABLED=0 GOOS=linux go test -c ./integration -o integration.test
           '
       - name: Upload hi binary
         if: steps.changed-files.outputs.files == 'true'
@@ -60,17 +58,12 @@ jobs:
           name: hi-binary
           path: hi
           retention-days: 10
-      - name: Package Go cache
-        if: steps.changed-files.outputs.files == 'true'
-        run: |
-          # Package Go module cache and build cache
-          tar -czf go-cache.tar.gz -C ~ go .cache/go-build
-      - name: Upload Go cache
+      - name: Upload integration test binary
         if: steps.changed-files.outputs.files == 'true'
         uses: actions/upload-artifact@330a01c490aca151604b8cf639adc76d48f6c5d4 # v5.0.0
         with:
-          name: go-cache
-          path: go-cache.tar.gz
+          name: integration-test-binary
+          path: integration.test
           retention-days: 10
       - name: Force overlay2 storage driver
         if: steps.changed-files.outputs.files == 'true'