Make guild member check case-insensitive in PR labeler (#54444)

Fixes the casing of the remaining names and adjust the script to allow
any casing of handles.

Release Notes:

- N/A

.github/workflows/pr_labeler.yml

@@ -37,6 +37,7 @@ jobs:
               '11happy',
               'AidanV',
               'AmaanBilwar',
+              'MostlyKIGuess',
               'OmChillure',
               'Palanikannan1437',
               'Shivansh-25',
@@ -60,7 +61,6 @@ jobs:
               'loadingalias',
               'marcocondrache',
               'mchisolm0',
-              'mostlyKIGuess',
               'nairadithya',
               'nihalxkumar',
               'notJoon',
@@ -114,7 +114,11 @@ jobs:
               return;
             }
 
-            if (GUILD_MEMBERS.includes(author)) {
+            const authorLower = author.toLowerCase();
+            const isGuildMember = GUILD_MEMBERS.some(
+              (member) => member.toLowerCase() === authorLower
+            );
+            if (isGuildMember) {
               await github.rest.issues.addLabels({
                 owner: context.repo.owner,
                 repo: context.repo.repo,