Use commits API instead of search API

The search API is rate limited much more than the normal API.
Also, the commits endpoint works on forks, and is simpler (returns
an empty list for unknown users, for example).

Both APIs only work on the default branch, but I think that should be fine.

src/github.rs

@@ -960,11 +960,6 @@ pub struct IssueSearchResult {
     pub items: Vec<Issue>,
 }
 
-#[derive(Debug, serde::Deserialize)]
-struct CommitSearchResult {
-    total_count: u32,
-}
-
 #[derive(Clone, Debug, serde::Deserialize)]
 pub struct Repository {
     pub full_name: String,
@@ -1534,33 +1529,24 @@ impl GithubClient {
     /// Returns whether or not the given GitHub login has made any commits to
     /// the given repo.
     pub async fn is_new_contributor(&self, repo: &Repository, author: &str) -> bool {
-        if repo.fork {
-            // GitHub always returns 0 results in forked repos, so this cannot
-            // work for them.
-            return false;
-        }
         let url = format!(
-            "{}/search/commits?q=repo:{}+author:{}",
+            "{}/repos/{}/commits?author={}",
             Repository::GITHUB_API_URL,
             repo.full_name,
             author,
         );
         let req = self.get(&url);
-        match self.json::<CommitSearchResult>(req).await {
-            Ok(res) => res.total_count == 0,
+        match self.json::<Vec<GithubCommit>>(req).await {
+            // Note: This only returns results for the default branch.
+            // That should be fine in most cases since I think it is rare for
+            // new users to make their first commit to a different branch.
+            Ok(res) => res.is_empty(),
             Err(e) => {
-                // 422 is returned for unknown user
-                if e.downcast_ref::<reqwest::Error>().map_or(false, |e| {
-                    e.status() == Some(StatusCode::UNPROCESSABLE_ENTITY)
-                }) {
-                    true
-                } else {
-                    log::warn!(
-                        "failed to search for user commits in {} for author {author}: {e}",
-                        repo.full_name
-                    );
-                    false
-                }
+                log::warn!(
+                    "failed to search for user commits in {} for author {author}: {e}",
+                    repo.full_name
+                );
+                false
             }
         }
     }