Remove psych dependency

[Sharpie]

Psych is a standard gem that is bundled with the Ruby installation and
thus having a pinned version forces Bundler/RV to re-compile a new copy
of something that is already present in the Ruby installation. This means
extra CPU cycles spent running C compilers and extra dependencies on -dev
packages to supply the required headers.

Psych was pinned to >= 4.0 in this commit to get consistent
YAML.safe_load behavior in older Ruby versions used by build pipelines:

puppetlabs/vanagon@463b0fb

This >= 4.0 requirement has been satisfied by the default gem set
since the release of Ruby 3.1.0, the minimum allowed Ruby version is
>= 3.2 since 4c4fe8a5, hence the original
reason for the pin is now moot.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document and added a Signed-off-by annotation to each of my commits
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[Sharpie]

Testing consisted of a full build of puppet-runtime-main and openvox-agent with the VANAGON_LOCATION environment variable set to a Git repo carrying this patch.

[bastelfreak]

we really need to get rubocop pinned or finally use voxpupuli-rubocop here :(

[Sharpie]

I opened PR #82 with Rubocop fixes