cmake: increase time-out for a long-running test

cmake: increase time-out for a long-running test

As suggested in
https://github.com/git-for-windows/git/issues/3966#issuecomment-1221264238,
t7112 can run for well over one hour, which seems to be the default
maximum run time at least when running CTest-based tests in Visual
Studio.

Let's increase the time-out as a stop gap to unblock developers wishing
to run Git's test suite in Visual Studio.

Note: The actual run time is highly dependent on the circumstances. For
example, in Git's CI runs, the Windows-based tests typically take a bit
over 5 minutes to run. CI runs have the added benefit that Windows
Defender (the common anti-malware scanner on Windows) is turned off,
something many developers are not at liberty to do on their work
stations. When Defender is turned on, even on this developer's high-end
Ryzen system, t7112 takes over 15 minutes to run.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>