Add link to diff between test coverage runs

Author: emlun

.github/actions/pit-results-comment/action.yml

@@ -49,7 +49,7 @@ runs:
           cp "${NEW_STATS_FILE}" "${PREV_STATS_FILE}"
         fi
 
-        ./.github/actions/pit-results-comment/stats-to-comment.sh "${PREV_STATS_FILE}" "${NEW_STATS_FILE}" "${{ inputs.prev-commit }}" > "${RESULTS_COMMENT_FILE}"
+        ./.github/actions/pit-results-comment/stats-to-comment.sh "${PREV_STATS_FILE}" "${NEW_STATS_FILE}" "${{ inputs.prev-commit }}" "${{ github.sha }}" > "${RESULTS_COMMENT_FILE}"
 
         curl -X POST \
            -H "Authorization: Bearer ${{ inputs.token }}" \

.github/actions/pit-results-comment/stats-to-comment.sh

@@ -63,10 +63,17 @@ EOF
     "${1}" "${2}" --raw-output
 
   if [[ -n "${3}" ]]; then
-    cat << EOF
+    if [[ -n "${4}" ]]; then
+      cat << EOF
 
 Previous run: ${3}
 EOF
+    else
+      cat << EOF
+
+Previous run: ${3} - [Diff](/${GITHUB_REPOSITORY}/compare/${3}...${4})
+EOF
+    fi
 
     cat << EOF