devops: fixed broken GitHub Actions workflow (#6399)

Author: mxschmitt

.github/workflows/tests.yml

@@ -59,7 +59,7 @@ jobs:
         node-version: 12
     - run: npm ci
       env:
-        DEBUG=extract-zip
+        DEBUG: extract-zip
     - run: npm run build
     - run: node lib/cli/cli install-deps ${{ matrix.browser }} chromium
     - run: npm run test -- --tag=${{ matrix.browser }}
@@ -88,7 +88,7 @@ jobs:
         node-version: 12
     - run: npm ci
       env:
-        DEBUG=extract-zip
+        DEBUG: extract-zip
     - run: npm run build
     - run: node lib/cli/cli install-deps
     - run: npm run test -- --tag=${{ matrix.browser }}
@@ -118,7 +118,7 @@ jobs:
         node-version: ${{ matrix.node_version }}
     - run: npm ci
       env:
-        DEBUG=extract-zip
+        DEBUG: extract-zip
     - run: npm run build
     - run: node lib/cli/cli install-deps
     - run: xvfb-run --auto-servernum --server-args="-screen 0 1280x960x24" -- bash packages/installation-tests/installation-tests.sh