[Arm64] Stop running Ubuntu16.04 arm64 Debug Build on PR (#28276)

Author: sdmaclea

netci.groovy

@@ -390,8 +390,14 @@ def targetGroupOsMapInnerloop = ['netcoreapp': ['Windows_NT', 'Ubuntu14.04', 'Ub
 
             // Set up triggers
             if (isPR) {
-                // We run Arm64 Debug and Linux Release as default PR builds
-                Utilities.addGithubPRTriggerForBranch(newJob, branch, "${osName} arm64 ${configurationGroup} Build")
+                if (configurationGroup == "Release") {
+                    // Run Arm64 Linux Release job automatically for PR builds
+                    Utilities.addGithubPRTriggerForBranch(newJob, branch, "${osName} arm64 ${configurationGroup} Build")
+                }
+                else {
+                    // Add Arm64 Linux Debug job hook
+                    Utilities.addGithubPRTriggerForBranch(newJob, branch, "${osName} arm64 ${configurationGroup} Build", "(?i).*test\\W+${osName}\\W+arm64\\W+${configurationGroup}.*")
+                }
             }
             else {
                 // Set a push trigger