reduce timeout for build job

Author: tvallin

.github/workflows/validate.yml

@@ -77,7 +77,7 @@ jobs:
           maven-cache: none
           run: etc/scripts/shellcheck.sh
   build:
-    timeout-minutes: 30
+    timeout-minutes: 15
     strategy:
       matrix:
         os: [ ubuntu-20.04, windows-2022 ]