diff: use csharp driver for better function headers in .cs files

Update .gitattributes to use the csharp pattern for hunk headers in *.cs files.
This will result in the csharp function name that a change occurs in to be
included in the hunk header.

.gitattributes

@@ -1,4 +1,5 @@
 ###############################################################################
 # Do not normalize any line endings.
 ###############################################################################
-* -text
+* -text
+*.cs diff=csharp