[Github] Make PR formatting job only run with C/C++ changes (#69556)

Currently the PR formatting job only runs clang-format. There isn't a
lot of utility in running it if there aren't any C/C++ changes as there
will be nothing to format. This isn't super noisy currently as the job
doesn't fail if there aren't any C/C++ changes, but it's a bit of a
waste.

In addition, this patch names the code formatting job "Check C++
Formatting" to make it clear that this job only checks C/C++ formatting
rather than Python formatting/other languages.

.github/workflows/pr-code-format.yml

@@ -1,10 +1,19 @@
 name: "Check code formatting"
-on: pull_request_target
+
+on:
+  pull_request_target:
+    paths:
+      - '**/*.cpp'
+      - '**/*.c'
+      - '**/*.h'
+      - '**/*.inc'
+
 permissions:
   pull-requests: write
 
 jobs:
-  code_formatter:
+  cpp_code_formatter:
+    name: "Check C++ Formatting"
     runs-on: ubuntu-latest
     steps:
       - name: Fetch LLVM sources