rubygems: latest - don't update RubyGems for Ruby head builds & Ruby < 2.2

Author: MSP-Greg

action.yml

@@ -12,7 +12,7 @@ inputs:
     description: |
       The version of RubyGems to use. Either 'default' (the default), 'latest', or a version number (e.g., 3.3.5).
       For 'default', no action is taken and the version of RubyGems that comes with Ruby by default is used.
-      For 'latest', `gem update --system` is run to update to the latest RubyGems version.
+      For 'latest', `gem update --system` is run to update to the proper latest RubyGems version.  Ruby head/master builds and Ruby 2.2 and earlier will not be updated.
       Similarly, if a version number is given, `gem update --system <version>` is run to update to that version of RubyGems, as long as that version is newer than the one provided by default.
   bundler:
     description: |

dist/index.js

@@ -1,3 +1,4 @@
+const common = require('./common')
 const path = require('path')
 const exec = require('@actions/exec')
 const semver = require('semver')
@@ -31,7 +32,9 @@ export async function rubygemsUpdate(rubygemsVersionInput, rubyPrefix, platform,
 
 async function rubygemsLatest(gem, platform, engine, version) {
   if (engine === 'ruby') {
-    if (version >= '3.0') {
+    if (common.isHeadVersion(version)) {
+      console.log('Ruby master builds use included RubyGems')
+    } else if (version >= '3.0') {
       await exec.exec(gem, ['update', '--system'])
     } else if (version >= '2.6') {
       await exec.exec(gem, ['update', '--system', '3.4.22'])