t5516: override MinGW-specific pwd override

This test is susceptible to MSys2's posix-to-windows path mangling; Let's
just use POSIX paths throughout and let the tests pass.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t5516-fetch-push.sh

@@ -16,6 +16,14 @@ This test checks the following functionality:
 
 . ./test-lib.sh
 
+if test_have_prereq MINGW
+then
+	# Avoid posix-to-windows path mangling
+	pwd () {
+		builtin pwd
+	}
+fi
+
 D=`pwd`
 
 mk_empty () {