Remove template syntax

Author: pquentin

.github/workflows/validate-pr.yml

@@ -19,7 +19,7 @@ jobs:
 
     steps:
       - name: Check pull request was opened from branch
-        if: ${{ github.event.pull_request.head.repo.full_name != 'elastic/elasticsearch-specification' }}
+        if: github.event.pull_request.head.repo.full_name != 'elastic/elasticsearch-specification'
         run: echo "Validation is not supported from forks"; exit 1
 
       - uses: actions/checkout@v4