ci: move coverity into nightly builds

Author: ethomson

.github/workflows/coverity.yml

@@ -235,3 +235,21 @@ jobs:
           ../ci/test.sh
         fi
       shell: bash
+
+  coverity:
+    name: Coverity
+    runs-on: ubuntu-latest
+    steps:
+    - name: Check out repository
+      uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - name: Download container
+      run: ci/getcontainer.sh ci/docker/xenial
+      env:
+        DOCKER_REGISTRY: ${{ env.docker-registry }}
+        GITHUB_TOKEN: ${{ secrets.github_token }}
+    - name: Run Coverity
+      run: ci/coverity.sh
+      env:
+        COVERITY_TOKEN: ${{ secrets.coverity_token }}