Revert GlobalState caching (#4006)

Right now we have consistent test setup within the same test class, so
caching the GlobalState within the same test class doesn't leak state.

But it's not easy to guarantee this for future tests and it can easily
become a footgun. So let's revert it for now.

Author: st0012

test/requests/support/expectations_test_runner.rb

@@ -8,14 +8,10 @@ class ExpectationsTestRunner < Minitest::Test
   TEST_PRISM_FIXTURES = File.join(TEST_FIXTURES_DIR, "prism/test/prism/fixtures/**", "*.txt")
 
   def setup
-    @global_state = self.class.shared_global_state
+    @global_state = RubyLsp::GlobalState.new
   end
 
   class << self
-    def shared_global_state
-      @shared_global_state ||= RubyLsp::GlobalState.new
-    end
-
     def expectations_tests(handler_class, expectation_suffix)
       class_eval(<<~RB, __FILE__, __LINE__ + 1)
         module ExpectationsRunnerMethods