Fix bug when list pull request commits (go-gitea#36485)

Fix go-gitea#36483 

In git log/rev-list, the "..." syntax represents the symmetric
difference between two references, which is different from the meaning
of "..." in git diff (where it implies diffing from the merge base).

For listing PR commits, we must use `merge-base..head` to include only
the commits introduced by the head branch. Otherwise, commits newly
pushed to the base branch would also be included, which is incorrect.

Author: lunny

services/git/compare.go

@@ -84,7 +84,11 @@ func GetCompareInfo(ctx context.Context, baseRepo, headRepo *repo_model.Reposito
 
 	// We have a common base - therefore we know that ... should work
 	if !fileOnly {
-		compareInfo.Commits, err = headGitRepo.ShowPrettyFormatLogToList(ctx, compareInfo.BaseCommitID+compareInfo.CompareSeparator+compareInfo.HeadCommitID)
+		// In git log/rev-list, the "..." syntax represents the symmetric difference between two references,
+		// which is different from the meaning of "..." in git diff (where it implies diffing from the merge base).
+		// For listing PR commits, we must use merge-base..head to include only the commits introduced by the head branch.
+		// Otherwise, commits newly pushed to the base branch would also be included, which is incorrect.
+		compareInfo.Commits, err = headGitRepo.ShowPrettyFormatLogToList(ctx, compareInfo.MergeBase+".."+compareInfo.HeadCommitID)
 		if err != nil {
 			return nil, fmt.Errorf("ShowPrettyFormatLogToList: %w", err)
 		}