Added upstream with https://github.com/OSGeo/grass/commit/47aa6e13ce62076f77dcb4cadb452ca6a57a00c6

--- lib/init/grass.py.orig
+++ lib/init/grass.py
@@ -295,7 +295,7 @@
     matches = []
     # https://docs.python.org/3/library/stdtypes.html#old-string-formatting
     for m in re.finditer(
-        "%([#0 +-]*)([0-9]*)(\.[0-9]*)?([hlL]?[diouxXeEfFgGcrsa%])", fmt
+        r"%([#0 +-]*)([0-9]*)(\.[0-9]*)?([hlL]?[diouxXeEfFgGcrsa%])", fmt
     ):
         matches.append(m)