Move the github context into environment variables

Move the github context under the run: configuration for the fetch step
into a set of environment variables under env: as they are empty within
run due to a currently known bug inside action runners.

action.yaml

@@ -7,14 +7,26 @@ description: |-
 runs:
   using: composite
   steps:
-    - run: |-
+
+    - name: Fetch the pull-requester artifact
+      shell: bash
+      env:
+        # Both github.action_repository and .action_ref are not available inside
+        # the run: statement, but they are available under env: so set them here
+        # so they can be accessed as normal environment variable under the
+        # run: statement instead. See the following for more information:
+        #   https://github.com/actions/runner/issues/2473
+        GH_ACTION_REPOSITORY: ${{ github.action_repository || github.repository }}
+        GH_ACTION_REF: ${{ github.action_ref || github.ref_name }}
+      run: |-
         ${{ github.action_path }}/scripts/fetch \
-          "${{ github.action_repository }}" \
-          "${{ github.action_ref }}"
+          "${GH_ACTION_REPOSITORY}" \
+          "${GH_ACTION_REF}"
+
+    - name: Run pull-requester against the pull request
       shell: bash
-    - run: |-
+      run: |-
         ${{ github.action_path }}/bin/pull-requester run
-      shell: bash
 
 branding:
   icon: user-check