CI: Fix services validator being unable to create Pull Requests

Add write permission to the pull-request scope for the
services-availability and services-validation jobs to allow them to
create and update Pull Requests.

.github/workflows/dispatch.yaml

@@ -38,6 +38,7 @@ jobs:
     permissions:
       checks: write
       contents: write
+      pull-requests: write
     steps:
       - uses: actions/checkout@v3
       - name: Check for Defunct Services 📉

.github/workflows/scheduled.yaml

@@ -16,6 +16,7 @@ jobs:
     permissions:
       checks: write
       contents: write
+      pull-requests: write
     steps:
       - uses: actions/checkout@v3
         with: