git_tools: add even more detail when commit fails

Follow-up to 32577b177e34bc7b23183df22d375c9ada146613
diff --git a/git_tools/git_tools.go b/git_tools/git_tools.go
index 242a8de..d047710 100644
--- a/git_tools/git_tools.go
+++ b/git_tools/git_tools.go
@@ -437,8 +437,8 @@
 	// Add the file to git
 	cmd = exec.CommandContext(ctx, "git", "add", filePath)
 	cmd.Dir = repoDir
-	if err := cmd.Run(); err != nil {
-		return fmt.Errorf("error adding file to git: %w", err)
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("error adding file to git: %w - git output: %s", err, string(out))
 	}
 
 	// Commit the changes