vim-patch:8.1.2182: test42 seen as binary by git diff #11256

Problem:    Test42 seen as binary by git diff.
Solution:   Add .gitattributes file.  Make explicit that 'cpo' does not
            contain 'S'. (Daniel Hahler, closes vim/vim#5072)
5b39d7adb0

.gitattributes

@@ -1 +1,2 @@
 *.h linguist-language=C
+src/nvim/testdir/test42.in diff