[CI] Make homebrew update job runnable on PR and push to master.

Because of a wrong path, the homebrew update could only run when
triggered as workflow.

Author: hageboeck

.github/workflows/update-brew-macs.yml

@@ -13,7 +13,13 @@ on:
     branches:
       - 'master'
     paths:
-      - '.github/workflow/update-brew-macs.yml'
+      - '.github/workflows/update-brew-macs.yml'
+
+  pull_request:
+    branches:
+      - 'master'
+    paths:
+      - '.github/workflows/update-brew-macs.yml'
 
 env:
   VENV_DIR: ${{ github.workspace }}/ROOT_CI_VENV