Condition labeling workflows to only run on dotnet/runtime.

Author: carlossanlop

.github/workflows/check-no-merge-label.yml

@@ -12,6 +12,7 @@ on:
 
 jobs:
   check-labels:
+    if: github.repository == 'dotnet/runtime'
     runs-on: ubuntu-latest
     steps:
     - name: Check 'NO-MERGE' label

.github/workflows/check-service-labels.yml

@@ -11,6 +11,7 @@ on:
 
 jobs:
   check-labels:
+    if: github.repository == 'dotnet/runtime'
     runs-on: ubuntu-latest
     steps:
     - name: Check 'Servicing-approved' label