ci: trigger workflows on PRs targeting cefpython147

The pull_request filter only listed "master", so workflows would not
run for pull requests opened against the cefpython147 branch. Add
cefpython147 to the pull_request branch filter in all three CI
workflows so the upstream maintainer can run CI on PRs into that
branch once the workflow files are present on the base branch.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: linesight

.github/workflows/ci-linux.yml

@@ -4,7 +4,7 @@ on:
   push:
     branches: ["master", "cefpython147"]
   pull_request:
-    branches: ["master"]
+    branches: ["master", "cefpython147"]
   workflow_dispatch:
     inputs:
       bypass_cache:

.github/workflows/ci-macos.yml

@@ -4,7 +4,7 @@ on:
   push:
     branches: ["master", "cefpython147"]
   pull_request:
-    branches: ["master"]
+    branches: ["master", "cefpython147"]
   workflow_dispatch:
     inputs:
       bypass_cache:

.github/workflows/ci-windows.yml

@@ -4,7 +4,7 @@ on:
   push:
     branches: [ "master", "cefpython147" ]
   pull_request:
-    branches: [ "master" ]
+    branches: [ "master", "cefpython147" ]
   workflow_dispatch:
     inputs:
       bypass_cache: