Switch imagePullPolicy to "IfNotPresent" (#568)

### Benefits

Less image pulls.

### Additional information

committed via GUI - so no signature on first commit.

Co-authored-by: pat-s <patrick.schratz@gmail.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/568
Reviewed-by: pat-s <pat-s@noreply.gitea.com>
Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-committed-by: justusbunsi <sk.bunsenbrenner@gmail.com>

unittests/config/server-section_domain.yaml

@@ -19,7 +19,7 @@ tests:
           path: stringData.server
           pattern: \nROOT_URL=http://git.example.com
 
-################################################
+  ################################################
 
   - it: "[no ingress hosts] uses gitea http service for DOMAIN|SSH_DOMAIN|ROOT_URL"
     template: templates/gitea/config.yaml
@@ -40,7 +40,7 @@ tests:
           path: stringData.server
           pattern: \nROOT_URL=http://gitea-unittests-http.testing.svc.cluster.local
 
-################################################
+  ################################################
 
   - it: "[provided via values] uses that for DOMAIN|SSH_DOMAIN|ROOT_URL"
     template: templates/gitea/config.yaml