grep: fix triggering PCRE2_NO_START_OPTIMIZE workaround

grep: fix triggering PCRE2_NO_START_OPTIMIZE workaround

PCRE2 bug 2642 was fixed in version 10.36.  Our 95ca1f987e (grep/pcre2:
better support invalid UTF-8 haystacks, 2021-01-24) worked around it on
older versions by setting the flag PCRE2_NO_START_OPTIMIZE.  797c359978
(grep/pcre2: use compile-time PCREv2 version test, 2021-02-18) switched
it around to set the flag on 10.36 and higher instead, while it claimed
to use "the same test done at compile-time".

Switch the condition back to apply the workaround on PCRE2 versions
_before_ 10.36.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>