[monitoring-plugins] Also add warn-on-use.h

[RincewindsHat]

 Module: monitoring-plugins
 Branch: update_gnulib_2021
 Commit: 9a1eb6988110a64cdeacb2072ce93eb0fc5150da
 Author: RincewindsHat <12514511+RincewindsHat at users.noreply.github.com>
   Date: Tue Aug 23 19:29:21 2022 +0200
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=9a1eb69

Also add warn-on-use.h

---

 .gitignore | 1 -
 1 file changed, 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index 86d5b2c..5e5373d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -87,7 +87,6 @@ NP-VERSION-FILE
 /gl/sys
 /gl/time.h
 /gl/unistd.h
-/gl/warn-on-use.h
 /gl/wchar.h
 /gl/wctype.h