(PA-5646) Move to self-hosted, older Ruby 2.7

Homebrew recently updated its Ruby 2.7 formula to use OpenSSL 3.0
instead of 1.1:

Homebrew/homebrew-core@fb4bb76

Ruby 2.7 does not support OpenSSL 3.0, so using Homebrew's updated
formula causes test failures for puppet-agent.

This commit switches our Vanagon projects to use the last version of
Homebrew's Ruby 2.7 formula prior to the switch over to OpenSSL 3.0,
hosted by Puppet.

Author: mhashizume

configs/components/_base-ruby.rb

@@ -59,9 +59,10 @@
 elsif platform.is_macos?
   pkg.environment 'optflags', settings[:cflags]
   if platform.is_cross_compiled?
-    # Pin to an older version of [email protected]. This can be removed once we're no longer cross-compiling
-    if ruby_version_y == "2.5"
-      pkg.build_requires "puppetlabs/puppet/[email protected]"
+    # Pin to an older version of [email protected] hosted by Puppet as Homebrew
+    # moved its Ruby 2.7 formula from OpenSSL 1.1 to 3.0
+    if ruby_version_y == "2.7"
+      pkg.build_requires "puppetlabs/puppet/[email protected]"
     else
       pkg.build_requires "ruby@#{ruby_version_y}"
     end