[CI] Update rules for applying tpu label. (#15634)

Signed-off-by: Russell Bryant <[email protected]>

Author: russellb

.github/mergify.yml

@@ -90,15 +90,34 @@ pull_request_rules:
 
 - name: label-tpu
   description: Automatically apply tpu label
+  # Keep this list in sync with `label-tpu-remove` conditions
   conditions:
     - or:
-      - files~=tpu
+      - files~=tpu.py
+      - files~=_tpu
+      - files~=tpu_
+      - files~=/tpu/
       - files~=pallas
   actions:
     label:
       add:
         - tpu
 
+- name: label-tpu-remove
+  description: Automatically remove tpu label
+  # Keep this list in sync with `label-tpu` conditions
+  conditions:
+    - and:
+      - -files~=tpu.py
+      - -files~=_tpu
+      - -files~=tpu_
+      - -files~=/tpu/
+      - -files~=pallas
+  actions:
+    label:
+      remove:
+        - tpu
+
 - name: ping author on conflicts and add 'needs-rebase' label
   conditions:
       - conflict