package/ruby: fix RUBY_VERSION_EXT

Correct RUBY_VERSION_EXT after commit be9783951d1d44 (package/ruby: security
bump to version 3.0.1):

ls output/target/usr/lib/ruby/
3.0.0  site_ruby  vendor_ruby

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 73e570a290374602814d53f8d3b2ca21079ad71a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/ruby/ruby.mk

@@ -6,7 +6,7 @@
 
 RUBY_VERSION_MAJOR = 3.0
 RUBY_VERSION = $(RUBY_VERSION_MAJOR).2
-RUBY_VERSION_EXT = 3.0.2
+RUBY_VERSION_EXT = 3.0.0
 RUBY_SITE = http://cache.ruby-lang.org/pub/ruby/$(RUBY_VERSION_MAJOR)
 RUBY_SOURCE = ruby-$(RUBY_VERSION).tar.xz
 RUBY_DEPENDENCIES = host-pkgconf host-ruby