CI: fixed on schedule workflows

- run on schedule only in CESNET/UltraGrid repo
- otherwise run only if pushing to respective branches
- run Coverity scan earlier (4:00 UTC)

.github/workflows/arm-build.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   Build:
-    if: github.repository == 'CESNET/UltraGrid' || github.event.schedule != null
+    if: github.repository == 'CESNET/UltraGrid' || github.event.schedule == null
     runs-on: ubuntu-latest
     strategy:
       matrix:

.github/workflows/coverity-scan.yml

@@ -5,10 +5,11 @@ on:
     branches:
       - coverity_scan
   schedule:
-   - cron:  '0 6 20 * *' # 20th at 6:00 UTC
+   - cron:  '0 4 20 * *' # 20th at 4:00 UTC
 
 jobs:
   Coverity:
+    if: github.repository == 'CESNET/UltraGrid' || github.event.schedule == null
     runs-on: ubuntu-latest
     env:
       SDK_URL: ${{ secrets.SDK_URL }}