Update Win_GPU_CI trigger (#13290)

### Description
supplement of #13248

Add PR trigger 

https://learn.microsoft.com/en-us/azure/devops/pipelines/repos/github?view=azure-devops&tabs=yaml#pr-triggers

fix: master -> main

Testted with #13289 #13292

NB:
the real pipeline is always triggered if the workflow yaml changed even
it's added in the path filter.

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->
Make sure the real pipeline not run in the backend.

.github/workflows/generated_fake_win_gpu_ci.yml

@@ -3,7 +3,7 @@
 
 name: Windows GPU CI Pipeline
 on:
-  push:
+  pull_request:
     paths:
       - docs/**
       - README.md

.github/workflows/skip-doc-change.yml.j2

@@ -3,7 +3,7 @@
 
 name: {{ ci_workflow_name }}
 on:
-  push:
+  pull_request:
     paths:
       - docs/**
       - README.md

tools/ci_build/github/azure-pipelines/win-gpu-ci-pipeline.yml

@@ -1,7 +1,18 @@
 trigger:
   branches:
     include:
-    - master
+    - main
+    - rel-*
+  paths:
+    exclude:
+    - docs/**
+    - README.md
+    - CONTRIBUTING.md
+    - BUILD.md
+pr:
+  branches:
+    include:
+    - main
     - rel-*
   paths:
     exclude: