Ignore failures when stopping postfix

.github/workflows/tests.yml

@@ -138,6 +138,7 @@ jobs:
           custom-cache-suffix: $(date -u -d "-0 month -$(($(date +%d)-1)) days" "+%F")
 
       # Install postfix and automatically retry if the install failed, which happens reguarly.
+      # We don't care if stopping postfix fails anyway
       # @link https://github.com/marketplace/actions/retry-step
       - name: Install postfix
         uses: nick-invision/retry@v2
@@ -147,7 +148,7 @@ jobs:
           retry_wait_seconds: 8
           command: |
             sudo apt-get install -y -qq postfix qmail
-            sudo service postfix stop
+            sudo service postfix stop || true
 
       - name: Set up sendmail
         run: |