Split GithubClient::graphql_query into two methods.

This adds a method to add a generic "errors" handler, so callers don't
need to worry about errors if they don't need specific ones.

This also drops the generic type, since it wasn't really used.

src/github.rs

@@ -2203,24 +2203,50 @@ impl GithubClient {
     }
 
     /// Issues an ad-hoc GraphQL query.
-    pub async fn graphql_query<T: serde::de::DeserializeOwned>(
+    ///
+    /// You are responsible for checking the `errors` array when calling this
+    /// function to determine if there is an error. Only use this if you are
+    /// looking for specific error codes, or don't care about errors. Use
+    /// [`GithubClient::graphql_query`] if you would prefer to have a generic
+    /// error message.
+    pub async fn graphql_query_with_errors(
         &self,
         query: &str,
         vars: serde_json::Value,
-    ) -> anyhow::Result<T> {
+    ) -> anyhow::Result<serde_json::Value> {
         self.json(self.post(&self.graphql_url).json(&serde_json::json!({
             "query": query,
             "variables": vars,
         })))
         .await
     }
 
+    /// Issues an ad-hoc GraphQL query.
+    ///
+    /// See [`GithubClient::graphql_query_with_errors`] if you need to check
+    /// for specific errors.
+    pub async fn graphql_query(
+        &self,
+        query: &str,
+        vars: serde_json::Value,
+    ) -> anyhow::Result<serde_json::Value> {
+        let result: serde_json::Value = self.graphql_query_with_errors(query, vars).await?;
+        if let Some(errors) = result["errors"].as_array() {
+            let messages: Vec<_> = errors
+                .iter()
+                .map(|err| err["message"].as_str().unwrap_or_default())
+                .collect();
+            anyhow::bail!("error: {}", messages.join("\n"));
+        }
+        Ok(result)
+    }
+
     /// Returns the object ID of the given user.
     ///
     /// Returns `None` if the user doesn't exist.
     pub async fn user_object_id(&self, user: &str) -> anyhow::Result<Option<String>> {
         let user_info: serde_json::Value = self
-            .graphql_query(
+            .graphql_query_with_errors(
                 "query($user:String!) {
                     user(login:$user) {
                         id
@@ -2273,7 +2299,7 @@ impl GithubClient {
         // work on forks. This GraphQL query seems to work fairly reliably,
         // and seems to cost only 1 point.
         match self
-            .graphql_query::<serde_json::Value>(
+            .graphql_query_with_errors(
                 "query($repository_owner:String!, $repository_name:String!, $user_id:ID!) {
                         repository(owner: $repository_owner, name: $repository_name) {
                             defaultBranchRef {