ci: tag capa-rules on release

Add GitHub Action to tag capa-rules when releasing capa. The used tag
name is the same as the one in capa.

.github/workflows/tag.yml

@@ -0,0 +1,24 @@
+name: tag
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  tag:
+    name: Tag capa rules
+    runs-on: ubuntu-20.04
+    steps:
+    - name: Checkout capa-rules
+      uses: actions/checkout@v2
+      with:
+        repository: fireeye/capa-rules
+        token: ${{ secrets.CAPA_TOKEN }}
+    - name: Tag capa-rules
+      run: git tag ${{ github.event.release.tag_name }}
+    - name: Push tag to capa-rules
+      uses: ad-m/github-push-action@master
+      with:
+        repository: fireeye/capa-rules
+        github_token: ${{ secrets.CAPA_TOKEN }}
+        tags: true