temporarily adding missing command coverage to cover for update command testing gap

Author: rosanch

src/azure-cli/azure/cli/command_modules/acr/linter_exclusions.yml

@@ -11,5 +11,9 @@ acr update:
         allow_trusted_services:
             rule_exclusions:
             - option_length_too_long
-
+acr connected-registry update:
+    parameters:
+        allow_trusted_services:
+            rule_exclusions:
+            - missing_command_test_coverage
 ...