t5705: the file:// URL should be absolute

The test misused a URL "file://." to mean "relative to here",
which we no longer accept.

In a file:// URL, typically there is no host, and RFC1738 says that
file:///<path> should be used.

Update t5705 to use a working URL.
Reported-by: NMichael Blume <blume.mike@gmail.com>
Signed-off-by: NTorsten Bögershausen <tboegi@web.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t5705-clone-2gb.sh

@@ -46,7 +46,7 @@ test_expect_success CLONE_2GB 'clone - bare' '
 
 test_expect_success CLONE_2GB 'clone - with worktree, file:// protocol' '
 
-	git clone file://. clone-wt
+	git clone "file://$(pwd)" clone-wt
 
 '