pgsql: ci: Enable PCH in mingw cross job

ci: Enable PCH in mingw cross job

This will make this job run a bit faster.

This backpatches commit 4075409de08 to 19. Since cirrus-ci shut down, only 19
and master have CI, due to the incremental work towards a new CI system. I
soon plan to backpatch CI to all versions that previously had CI. Maintenance
of CI going forward will be simpler if the branches are as similar as
possible.

Co-authored-by: Andres Freund <andres(at)anarazel(dot)de>
Reviewed-by: Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/e52e2c29-4834-4c64-a200-eddcba38fb4d%40eisentraut.org
Backpatch-through: 19

Branch
------
REL_19_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/df7a12749fbe39930be1de871e504325d6e5a5f1
Author: Peter Eisentraut <peter(at)eisentraut(dot)org>

Modified Files
--------------
.github/workflows/pg-ci.yml | 3 +++
1 file changed, 3 insertions(+)