pgsql: ci: openbsd: Increase RAM disk's size

ci: openbsd: Increase RAM disk's size

Its size was ~3.8GB before, which sometimes was not enough. OpenBSD CI task
often were failing due to no space left on device. Increase the RAM disk size
to ~4.6 GB.

Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/CAN55FZ2XVVPJRJmGB2DsL3gOrOinWh=HWvj6GO1cHzJ=6LwTag@mail.gmail.com
Backpatch-through: 18, where openbsd was added to CI

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/20d541a200e9dfed8affef9e798ff35ca0f30b8e

Modified Files
--------------
src/tools/ci/gcp_ram_disk.sh | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)