Use three-dot diffs in URL and xref lint workflows (#10706)

Author: shoumikhin

.github/workflows/_link_check.yml

@@ -7,6 +7,7 @@ on:
 
 jobs:
   lint-urls:
+    if: ${{ github.event_name != 'pull_request' || !contains(github.event.pull_request.labels.*.name, 'skip-url-lint') }}
     uses: pytorch/test-infra/.github/workflows/linux_job_v2.yml@main
     with:
       runner: linux.2xlarge
@@ -17,13 +18,15 @@ jobs:
       timeout: 90
       script: |
         ./scripts/lint_urls.sh $(
-          [ "${{ github.event_name }}" = "pull_request" ] \
-            && git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} \
-          || [ "${{ github.event_name }}" = "push" ] \
-            && git diff --name-only ${{ github.event.before }} ${{ github.sha }}
+          { [ "${{ github.event_name }}" = "pull_request" ] \
+              && git diff --name-only "${{ github.event.pull_request.base.sha }}...${{ github.event.pull_request.head.sha }}"; } \
+          || \
+          { [ "${{ github.event_name }}" = "push" ] \
+              && git diff --name-only "${{ github.event.before }}...${{ github.sha }}"; }
         )
 
   lint-xrefs:
+    if: ${{ github.event_name != 'pull_request' || !contains(github.event.pull_request.labels.*.name, 'skip-xref-lint') }}
     uses: pytorch/test-infra/.github/workflows/linux_job_v2.yml@main
     with:
       runner: linux.2xlarge
@@ -34,8 +37,9 @@ jobs:
       timeout: 90
       script: |
         ./scripts/lint_xrefs.sh $(
-          [ "${{ github.event_name }}" = "pull_request" ] \
-            && git diff --name-only ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} \
-          || [ "${{ github.event_name }}" = "push" ] \
-            && git diff --name-only ${{ github.event.before }} ${{ github.sha }}
+          { [ "${{ github.event_name }}" = "pull_request" ] \
+              && git diff --name-only "${{ github.event.pull_request.base.sha }}...${{ github.event.pull_request.head.sha }}"; } \
+          || \
+          { [ "${{ github.event_name }}" = "push" ] \
+              && git diff --name-only "${{ github.event.before }}...${{ github.sha }}"; }
         )