t5580: enable UNC path tests also for lower-case drive letters

UNC path tests are run only when the trash directory is on a path that
can be mangled into an UNC path. For this, a drive letter is necessary.
The protection checks only for upper-case drive letters, but lower-case
drive letters work just fine as well.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>

Author: j6t

t/t5580-unc-paths.sh

@@ -19,7 +19,7 @@ fi
 
 UNCPATH="$(winpwd)"
 case "$UNCPATH" in
-[A-Z]:*)
+[A-Za-z]:*)
 	# Use administrative share e.g. \\localhost\C$\git-sdk-64\usr\src\git
 	# (we use forward slashes here because MSYS2 and Git accept them, and
 	# they are easier on the eyes)