gifn-apply: tox.ini: convert to the Tox 4.x format

Change-Id: I0df79f78a9d5adcda1e11a1d8f50a98e5c7f51d8
diff --git a/tools/git-if-needed/tox.ini b/tools/git-if-needed/tox.ini
index ad40b73..3351089 100644
--- a/tools/git-if-needed/tox.ini
+++ b/tools/git-if-needed/tox.ini
@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: BSD-2-Clause
 
 [tox]
+minversion = 4.1
 envlist =
   ruff
   ruff-all
@@ -15,7 +16,7 @@
 
 [defs]
 pyfiles =
-  python/gifn_apply
+  python/gifn_apply \
   python/unit_tests
 
 [testenv:black]