Improve error message for SCM command failures

The error message for failures in the SCM command execution has been enhanced. Now it displays not only the command's return code but also the standard output and error, improving the debugging process.

bumpversion/scm.py

@@ -76,7 +76,8 @@ def commit(cls, message: str, current_version: str, new_version: str, extra_args
             if isinstance(exc, TypeError):
                 err_msg = f"Failed to run {cls._COMMIT_COMMAND}: {exc}"
             else:
-                err_msg = f"Failed to run {exc.cmd}: return code {exc.returncode}, output: {exc.output}"
+                output = "\n".join([x for x in [exc.stdout, exc.stderr] if x])
+                err_msg = f"Failed to run {exc.cmd}: return code {exc.returncode}, output: {output}"
             logger.exception(err_msg)
             raise BumpVersionError(err_msg) from exc
         finally: