person_ops.gql: move @check to a field with no side effects.

Adding `@check` to a field with side effects became illegal since cl/756896487. The fix in this commit adds a "query" field (which has no side effects) and, instead, attaches the `@check` directive to that.

This fixes the following 2 test failures in `OperationExecutionErrorsIntegrationTest`:
* `executeMutationFailsWithNonNullDataNonEmptyErrorsDecodingSucceeds`
* `executeMutationFailsWithNonNullDataNonEmptyErrorsDecodingFails`

The test failures looked like this:

```
io.kotest.assertions.MultiAssertionError: The following 2 assertions failed:

1) exception.message
"operation encountered errors during execution: [mutation.createPersonWithPartialFailure.person2: @check is disallowed on side-effect fields unless the operation has @transaction]" should contain the substring "ecxpjy4qfy" with non-abutting text
   at com.google.firebase.dataconnect.testutil.TestUtilsKt.shouldContainWithNonAbuttingText(TestUtils.kt:79)

2) exception.response.rawData
Expected [("person1", [("id", "com.google.firebase.dataconnect.OperationExecutionErrorsIntegrationTest.executeMutationFailsWithNonNullDataNonEmptyErrorsDecodingFails_vNGzY61U2l3DkpBiK4s1")]), ("person2", <null>)] but actual was null

   at com.google.firebase.dataconnect.testutil.DataConnectOperationExceptionTestUtilsKt.shouldSatisfy(DataConnectOperationExceptionTestUtils.kt:74)
	at com.google.firebase.dataconnect.testutil.DataConnectOperationExceptionTestUtilsKt.shouldSatisfy(DataConnectOperationExceptionTestUtils.kt:266)
	at com.google.firebase.dataconnect.OperationExecutionErrorsIntegrationTest$executeMutationFailsWithNonNullDataNonEmptyErrorsDecodingFails$1.invokeSuspend(OperationExecutionErrorsIntegrationTest.kt:224)
```

Author: dconeybe

firebase-dataconnect/emulator/dataconnect/connector/person/person_ops.gql

@@ -96,6 +96,7 @@ query getPersonWithPartialFailure($id: String!) @auth(level: PUBLIC) {
 
 mutation createPersonWithPartialFailure($id: String!, $name: String!) @auth(level: PUBLIC) {
   person1: person_insert(data: { id: $id, name: $name })
-  person2: person_insert(data: { id_expr: "uuidV4()", name: $name }) @check(expr: "false", message: "ecxpjy4qfy")
+  query @redact { person(id: $id) { id @check(expr: "false", message: "ecxpjy4qfy") } }
+  person2: person_insert(data: { id_expr: "uuidV4()", name: $name })
 }