LU-15010 tests: skip sanity test_64g for interop

LU-15010 tests: skip sanity test_64g for interop

Sanity test_64g checks code that was only added in 2.14.56.

Test-Parameters: trivial serverversion=2.14.0 testlist=sanity env=ONLY=64g
Fixes: 6e116213e3fd ("LU-15010 mdc: add support for grant shrink")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I339231f1b7890e8fffe7e079a052b15f54d4a050
Reviewed-on: https://review.whamcloud.com/46565
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alena Nikitenko <anikitenko@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>