[ruby/rack] Use Ruby 3.4-rc (#9066)

Passenger doesn't seem to support Ruby 3.4 yet.

+-----+-------------------------+---------+------+------+-----+-----+-------+--------------+
| name|              branch_name|plaintext|update|  json|   db|query|fortune|weighted_score|
+-----+-------------------------+---------+------+------+-----+-----+-------+--------------+
| rack|                   master|   122790| 12419|114056|31397|17953|  22416|          1519|
| rack|         rack/ruby-3.4-rc|   129116| 16564|134504|44139|23214|  30169|          1992|
+-----+-------------------------+---------+------+------+-----+-----+-------+--------------+

frameworks/Ruby/rack-sequel/rack-sequel-postgres-unicorn-mri.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ADD ./ /rack-sequel
 

frameworks/Ruby/rack-sequel/rack-sequel-postgres.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ADD ./ /rack-sequel
 

frameworks/Ruby/rack-sequel/rack-sequel-unicorn-mri.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ADD ./ /rack-sequel
 

frameworks/Ruby/rack-sequel/rack-sequel.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ADD ./ /rack-sequel
 

frameworks/Ruby/rack/rack-falcon.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ENV RUBY_YJIT_ENABLE=1
 

frameworks/Ruby/rack/rack-unicorn.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ENV RUBY_YJIT_ENABLE=1
 

frameworks/Ruby/rack/rack.dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:3.3
+FROM ruby:3.4-rc
 
 ENV BUNDLE_FORCE_RUBY_PLATFORM=true
 ENV RUBY_YJIT_ENABLE=1