Replace pull_request_target event from docs workflow (#15526)

.github/workflows/docs-checks.yml

@@ -4,9 +4,7 @@ name: Check Docs
 on:
   push:
     branches: ["master", "release/*"]
-  # use this event type to share secrets with forks.
-  # it's important that the PR head SHA is checked out to run the changes
-  pull_request_target:
+  pull_request:
     branches: ["master", "release/*"]
     paths:
       - ".actions/**"
@@ -32,8 +30,6 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v3
-        with:
-          ref: ${{ github.event.pull_request.head.sha }}
       - uses: actions/setup-python@v4
         with:
           python-version: "3.8"
@@ -60,7 +56,6 @@ jobs:
       - uses: actions/checkout@v3
         with:
           submodules: true
-          ref: ${{ github.event.pull_request.head.sha }}
       - uses: actions/download-artifact@v3
         with:
           name: ci-packages-${{ github.sha }}
@@ -135,7 +130,6 @@ jobs:
       - uses: actions/checkout@v3
         with:
           submodules: true
-          ref: ${{ github.event.pull_request.head.sha }}
       - uses: actions/download-artifact@v3
         with:
           name: ci-packages-${{ github.sha }}