Don't relabel to a team if there is already a team label

Author: jackh726

triagebot.toml

@@ -113,6 +113,9 @@ trigger_files = [
     "src/tools/rustdoc-js",
     "src/tools/rustdoc-themes",
 ]
+exclude_labels = [
+    "T-*",
+]
 
 [autolabel."T-compiler"]
 trigger_files = [
@@ -122,6 +125,9 @@ trigger_files = [
     # Tests
     "src/test/ui",
 ]
+exclude_labels = [
+    "T-*",
+]
 
 [notify-zulip."I-prioritize"]
 zulip_stream = 245100 # #t-compiler/wg-prioritization/alerts