Adding back the pull_request trigger to the workflow

In order to have the RIT tests working as we have it today, we need to add triggers for
every commit and for when the PR is opened, but only for masters and *-rc branches base branches.

.github/workflows/rit.yml

@@ -3,6 +3,9 @@ name: Rootstock Integration Tests
 on:
   push:
     branches: ["master", "*-rc"]
+  pull_request:
+    types: [ opened, synchronize, reopened ]
+    branches: [ "master", "*-rc" ]
   workflow_dispatch:
     inputs:
       rit-branch:
@@ -32,6 +35,8 @@ jobs:
             POWPEG_BRANCH="${{ github.ref }}"
           elif [[ "${{ github.event_name }}" == "workflow_dispatch" ]]; then
             POWPEG_BRANCH="${{ github.ref_name }}"
+          elif [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            POWPEG_BRANCH="${{ github.head_ref }}"
           fi
 
           echo "RSKJ_BRANCH=$RSKJ_BRANCH" >> $GITHUB_ENV