t9210, t9211: disable GIT_TEST_SPLIT_INDEX for scalar clone tests

t9210, t9211: disable GIT_TEST_SPLIT_INDEX for scalar clone tests

index.skipHash (Scalar default) and split-index are incompatible:
the shared index gets a null OID when skipHash skips computing the
hash, and the null OID causes the shared index to not be loaded on
re-read.  This triggers a BUG assertion in fsmonitor when the
fsmonitor_dirty bitmap references more entries than the (now empty)
index has.

Disable GIT_TEST_SPLIT_INDEX in the scalar clone tests that hit
this: tests 12, 13, and 22 in t9210 (matching the existing
workaround in test 16), and all of t9211 (every test does scalar
clone).

Signed-off-by: Paul Tarjan <github@paulisageek.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>