Disable Ruby 3.1 shorthand Hash syntax

What does this MR do and why?

Ruby 3.1 introduced a new short-hand syntax for passing keyword arguments:

val = 42
m(val: val)

can now be:

val = 42
m(val:) # passes `val`

However, this will break backwards compatibility with Ruby 3.0, so let's disable this for now.

Relates to gitlab-org/gitlab#396229 (closed)