Prevent Firefox from using apple-touch-icon (#10402)

* Prevent Firefox from using apple-touch-icon

The opaque background does not work well in Firefox which uses the icon
as a "rich icon". Prevent this by not specifying it in HTML. Real Apple
devices will still request the icon on the static path.

Fixes: https://github.com/go-gitea/gitea/issues/10394

Also adjust gitignore so app.ini.sample becomes searchable and fixed a
variable name in app.ini.sample.

* fix gitignore

.gitignore

@@ -49,7 +49,10 @@ coverage.all
 
 /bin
 /dist
-/custom
+/custom/*
+!/custom/conf
+/custom/conf/*
+!/custom/conf/app.ini.sample
 /data
 /indexers
 /log