Require Ruby >= 3.0 (#435)

* Require Ruby >= 3.0.0

* Update test.yml

Author: HarlemSquirrel

.github/workflows/test.yml

@@ -23,7 +23,6 @@ jobs:
           - "3.1"
           - "3.2"
           - "3.3"
-          - "jruby-9.3"
           - "jruby-9.4"
           - "truffleruby"
     steps:

net-ldap.gemspec

@@ -26,7 +26,7 @@ the most recent LDAP RFCs (4510-4519, plutions of 4520-4532).}
   s.homepage = %q{http://github.com/ruby-ldap/ruby-net-ldap}
   s.rdoc_options = ["--main", "README.rdoc"]
   s.require_paths = ["lib"]
-  s.required_ruby_version = ">= 2.0.0"
+  s.required_ruby_version = ">= 3.0.0"
   s.summary = %q{Net::LDAP for Ruby (also called net-ldap) implements client access for the Lightweight Directory Access Protocol (LDAP), an IETF standard protocol for accessing distributed directory services}
 
   s.add_dependency("ostruct")