i915/gt/selftests: Disable lrc_timestamp test

i915/gt/selftests: Disable lrc_timestamp test

This test was designed to isolate a bug in tigerlake and dg2 hardware.
The bug was found and fixed in newer generations.
Since we won't support any new hardware with this driver, the test
should now be turned off in the CI to not pollute it with random failures
on previous hardware.

For reference, the issue has been discssued here[*].

[*] https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13697

Signed-off-by: Mikolaj Wasiak <mikolaj.wasiak@intel.com>
Reviewed-by: Chris Wilson <chris.p.wilson@linux.intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/uxxb22n667zb3aic6zs4mr2krv5zavav5v2zjgqnhnabgxgzif@4icszicjakex