[CI] run everything for branches/tags (elastic#20057)

Jenkinsfile

@@ -1146,11 +1146,18 @@ def reportCoverage(){
   }
 }
 
-// isChanged treats the patterns as regular expressions. In order to check if
-// any file in a directoy is modified use `^<path to dir>/.*`.
+/**
+*  isChanged treats the patterns as regular expressions. In order to check if
+*  any file in a directoy is modified use `^<path to dir>/.*`.
+*
+*  In addition, there are another two alternatives to report that there are
+*  changes, when `runAllStages` parameter is set to true or when running on a
+*  branch/tag basis.
+*/
 def isChanged(patterns){
   return (
-    params.runAllStages
+    params.runAllStages   // when runAllStages UI parameter is set to true
+    || !isPR()            // when running on a branch/tag
     || isGitRegionMatch(patterns: patterns, comparator: 'regexp')
   )
 }