ci : add OpenCL to labeler workflow (#14496)

Author: CISC

.github/labeler.yml

@@ -93,3 +93,8 @@ Ascend NPU:
             - ggml/include/ggml-cann.h
             - ggml/src/ggml-cann/**
             - docs/backend/CANN.md
+OpenCL:
+    - changed-files:
+        - any-glob-to-any-file:
+            - ggml/include/ggml-opencl.h
+            - ggml/src/ggml-opencl/**