ci: pin Linux build RIDs across stages and retry runtime fetches [CI]

scripts/test-linux-agent-build.py

@@ -65,6 +65,9 @@ class LinuxBuildTests(unittest.TestCase):
             self.assertIn('Targets="Restore" BuildInParallel="false"', traversal)
             self.assertIn('Targets="Build" BuildInParallel="false"', traversal)
             self.assertIn('RuntimeIdentifier=$(RuntimeIdentifier);SelfContained=$(SelfContained)', traversal)
+            containerfile = (first / 'Containerfile').read_text()
+            self.assertIn('test -n "$NODE_RID"', containerfile)
+            self.assertIn('-p:RuntimeIdentifier="$NODE_RID"', containerfile)
 
     def test_retention_removes_only_expired_layers_without_pruning_package_caches(self):
         with tempfile.TemporaryDirectory() as directory: