Update github actions. Add slack notifications

.github/workflows/veraPDF_WebApp_CI_with_Maven.yml

@@ -10,7 +10,7 @@ name: Java CI with Maven for veraPDF WebApp
 
 on:
   schedule:
-      - cron: "05 02 * * 1"
+      - cron: "05 09 * * 1"
   push:
     branches: [ "master" ]
   # pull_request:
@@ -61,3 +61,23 @@ jobs:
       with:
         name: Results
         path: "./target"
+
+    - name: Notify slack tests succeded
+      if: success()
+      env:
+        SLACK_BOT_TOKEN: ${{ secrets.SLACK_NOTIFICATIONS_BOT_TOKEN }}
+      uses: voxmedia/github-action-slack-notify-build@v1
+      with:
+        channel_id: C03E3JJGLQL
+        status: SUCCESS
+        color: good
+
+    - name: Notify slack tests failed
+      if: failure()
+      env:
+        SLACK_BOT_TOKEN: ${{ secrets.SLACK_NOTIFICATIONS_BOT_TOKEN }}
+      uses: voxmedia/github-action-slack-notify-build@v1
+      with:
+        channel_id: C03E3JJGLQL
+        status: FAILED
+        color: danger