Update "front_matter_parser" to be compatible with Psych 4. Psych 4 is the version included in Ruby 3.1. See https://github.com/waiting-for-dev/front_matter_parser/pull/11.
"front_matter_parser" was explicitly locked at 1.0.0 in Administrate in #2023 to avoid an incompatibility with Ruby 2.5.
Then it was unlocked in #2027 when support for Ruby 2.5 was dropped.
However, front_matter_parser was also dependabot-ignored in https://github.com/thoughtbot/administrate/pull/2021#issuecomment-886107091, and I think it was never un-ignored, so dependabot hasn't suggested an upgrade.
I believe if we update it via this PR then dependabot will automatically start monitoring it again.