Fix `/repos/{owner}/{repo}/pulls/{index}/files` endpoint not populating `previous_filename` (#32017) (#32028)

Backport #32017 by @charles-plutohealth

---
`status == "rename"` should have read `status == "renamed"`. The typo
means that file.PreviousFilename would never be populated, which e.g.
breaks usage of the Github Action at
https://github.com/dorny/paths-filter.

Co-authored-by: charles-plutohealth <143208583+charles-plutohealth@users.noreply.github.com>

services/convert/convert.go

@@ -424,6 +424,7 @@ func ToLFSLock(ctx context.Context, l *git_model.LFSLock) *api.LFSLock {
 // ToChangedFile convert a gitdiff.DiffFile to api.ChangedFile
 func ToChangedFile(f *gitdiff.DiffFile, repo *repo_model.Repository, commit string) *api.ChangedFile {
 	status := "changed"
+	previousFilename := ""
 	if f.IsDeleted {
 		status = "deleted"
 	} else if f.IsCreated {
@@ -432,6 +433,7 @@ func ToChangedFile(f *gitdiff.DiffFile, repo *repo_model.Repository, commit stri
 		status = "copied"
 	} else if f.IsRenamed && f.Type == gitdiff.DiffFileRename {
 		status = "renamed"
+		previousFilename = f.OldName
 	} else if f.Addition == 0 && f.Deletion == 0 {
 		status = "unchanged"
 	}
@@ -442,14 +444,11 @@ func ToChangedFile(f *gitdiff.DiffFile, repo *repo_model.Repository, commit stri
 		Additions:        f.Addition,
 		Deletions:        f.Deletion,
 		Changes:          f.Addition + f.Deletion,
+		PreviousFilename: previousFilename,
 		HTMLURL:          fmt.Sprint(repo.HTMLURL(), "/src/commit/", commit, "/", util.PathEscapeSegments(f.GetDiffFileName())),
 		ContentsURL:      fmt.Sprint(repo.APIURL(), "/contents/", util.PathEscapeSegments(f.GetDiffFileName()), "?ref=", commit),
 		RawURL:           fmt.Sprint(repo.HTMLURL(), "/raw/commit/", commit, "/", util.PathEscapeSegments(f.GetDiffFileName())),
 	}
 
-	if status == "rename" {
-		file.PreviousFilename = f.OldName
-	}
-
 	return file
 }