pgsql: meson: Add missing argument to gssapi.h check

meson: Add missing argument to gssapi.h check

These were missing since the initial introduction of the meson based build, in
e6927270cd18. As-is this is unlikely to cause an issue, but a future commit
will add support for detecting gssapi without use of dependency(), which could
fail due to this.

Discussion: https://postgr.es/m/20240708225659.gmyqoosi7km6ysgn@awork3.anarazel.de
Backpatch: 16-, where the meson based build was added

Branch
------
REL_17_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/5b707bb507bdc9b8bf120db1a0f7dad4cdb78e46

Modified Files
--------------
meson.build | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)