Made comparison case insensitive, pointed this out in the help text

Added an extra test case for the case insensitive scenario

Author: pbalint-ge

src/main/java/com/cloudbees/jenkins/GitHubPushTrigger.java

@@ -54,6 +54,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
 import java.util.Set;
@@ -105,18 +106,24 @@ public void onPost(final GitHubTriggerEvent event) {
             return; // nothing to do
         }
         if (useGitExcludedUsers) {
-            Set<String> excludedUsers = null;
+            Set<String> lowercaseExcludedUsers = new HashSet<>();
             if (job instanceof AbstractProject) {
                 SCM scm = ((AbstractProject<?, ?>) job).getScm();
                 if (scm instanceof GitSCM) {
                     UserExclusion exclusions = ((GitSCM) scm).getExtensions().get(UserExclusion.class);
                     if (exclusions != null) {
-                        excludedUsers = exclusions.getExcludedUsersNormalized();
+                        for (String userName: exclusions.getExcludedUsersNormalized()) {
+                            lowercaseExcludedUsers.add(userName.toLowerCase());
+                        }
                     }
                 }
             }
 
-            if (excludedUsers != null && excludedUsers.contains(event.getTriggeredByUser())) {
+            String lowercaseTriggeredByUser = null;
+            if (event.getTriggeredByUser() != null) {
+                lowercaseTriggeredByUser = event.getTriggeredByUser().toLowerCase();
+            }
+            if (lowercaseExcludedUsers != null && lowercaseExcludedUsers.contains(lowercaseTriggeredByUser)) {
                 return; // user is excluded from triggering build
             }
         }

src/main/resources/com/cloudbees/jenkins/GitHubPushTrigger/config.groovy

@@ -22,5 +22,5 @@ InlineWarning.setup({
 }
 
 f.entry() {
-    f.checkbox(title: _("Use Git excluded user list (\"Polling ignores commits from certain users\")"), field: "useGitExcludedUsers")
+    f.checkbox(title: _("Use Git excluded user list (\"Polling ignores commits from certain users\", comparison is case insensitive)"), field: "useGitExcludedUsers")
 }

src/test/java/com/cloudbees/jenkins/GitHubPushTriggerTest.java

@@ -145,6 +145,33 @@ public void shouldSkipBuildIfExclusionEnabledWithMatchingUser() throws IOExcepti
         verify(spiedQueue, times(0)).execute(Mockito.any(Runnable.class));
     }
 
+    @Test
+    public void shouldSkipBuildIfExclusionEnabledWithMatchingUserCaseInsensitive() throws IOException {
+        SequentialExecutionQueue spiedQueue = addSpyToQueueField();
+
+        String matchingUserName = "userName".toLowerCase();
+        FreeStyleProject project = jRule.createFreeStyleProject();
+        GitHubPushTrigger trigger = new GitHubPushTrigger();
+        trigger.setUseGitExcludedUsers(true);
+        trigger.start(project, false);
+        project.addTrigger(trigger);
+        GitSCM scm = new GitSCM("https://localhost/dummy.git");
+        UserExclusion userExclusion = new UserExclusion("something" + System.lineSeparator() +
+                                                        matchingUserName.toUpperCase() + System.lineSeparator() +
+                                                        "somethingElse" + System.lineSeparator()); 
+        scm.getExtensions().add(userExclusion);
+        project.setScm(scm);
+        
+        GitHubTriggerEvent event = GitHubTriggerEvent.create()
+                                                     .withTimestamp(System.currentTimeMillis())
+                                                     .withOrigin("origin")
+                                                     .withTriggeredByUser(matchingUserName)
+                                                     .build();
+        trigger.onPost(event);
+        
+        verify(spiedQueue, times(0)).execute(Mockito.any(Runnable.class));
+    }
+
     @Test
     public void shouldTriggerBuildIfExclusionEnabledWithNonMatchingUser() throws IOException {
         SequentialExecutionQueue spiedQueue = addSpyToQueueField();