GitHubPusher: add commits instead of resetting branch

Deleting and recreating the branch causes GitHub to close the
associated PR. Force-updating has the same effect on PR history.
Instead, only create the branch when it doesn't exist and commit
on top, so the PR stays open and accumulates commits naturally.

follow-up: #132

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: sorah

app/jobs/generate_sponsors_yaml_file_job.rb

@@ -169,26 +169,23 @@ def push
         return
       end
 
-      reset_branch
+      ensure_branch
       commit_content
       create_or_update_pull_request
     end
 
     private
 
-    def reset_branch
-      begin
-        octokit.delete_branch(@repo.name, @branch_name)
-      rescue Octokit::UnprocessableEntity
-      end
-
-      head = octokit.branch(@repo.name, base_branch)
-      octokit.create_ref(@repo.name, "refs/heads/#{@branch_name}", head[:commit][:sha])
+    def ensure_branch
+      octokit.branch(@repo.name, @branch_name)
+    rescue Octokit::NotFound
+      head_sha = octokit.branch(@repo.name, base_branch)[:commit][:sha]
+      octokit.create_ref(@repo.name, "refs/heads/#{@branch_name}", head_sha)
     end
 
     def commit_content
       begin
-        blob_sha = octokit.contents(@repo.name, path: @filepath, ref: base_branch)[:sha]
+        blob_sha = octokit.contents(@repo.name, path: @filepath, ref: @branch_name)[:sha]
       rescue Octokit::NotFound
         blob_sha = nil
       end