Add test issue_comment workflow

.github/workflows/issue_comment.yml

@@ -0,0 +1,46 @@
+# Run integration tests when a maintainer comments `!test` on a PR to feature branch
+# Fails when base branch is `main`, as it doesn't support e2e tests
+name: End to end integration tests
+
+on:
+  issue_comment:
+    types: [created]
+
+jobs:
+  integration-tests-e2e:
+    name: E2E verification
+    runs-on: buildjet-16vcpu-ubuntu-2204
+    if:
+      github.event.issue.pull_request
+      && github.event.issue.state == 'open'
+      && contains(github.event.comment.body, '!test')
+      && (github.event.comment.author_association == 'MEMBER' || github.event.comment.author_association == 'OWNER')
+    steps:
+      - uses: xt0rted/pull-request-comment-branch@v2
+        id: comment-branch
+
+      - name: Exit if base branch is `main`
+        if: ${{ steps.comment-branch.outputs.base_ref == 'main' }}
+        run: |
+          echo "Cannot run end2end integration tests on PR targeting `main`"
+          exit 1
+        continue-on-error: false
+
+      - uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Checkout PR branch
+        run: gh pr checkout $PR_NUMBER
+        env:
+          GH_TOKEN: ${{ github.token }}
+          PR_NUMBER: ${{ github.event.issue.number }}
+
+      - name: Comment on successful run
+        uses: peter-evans/create-or-update-comment@v3
+        with:
+          issue-number: ${{ github.event.issue.number }}
+          body: |
+            End-to-end `!test` action succeeded! :rocket:
+
+            https://github.com/lurk-lab/solidity-verifier/actions/runs/${{ github.run_id }}