use one-line pattern matching for warning tests

spec/ruby/command_line/dash_upper_w_spec.rb

@@ -32,7 +32,7 @@ ruby_version_is "2.7" do
 
   describe "The -W command line option with :no-experimental" do
     it "suppresses experimental warnings" do
-      result = ruby_exe('case 0; in a; end', args: '2>&1')
+      result = ruby_exe('1 => a', args: '2>&1')
       result.should =~ /is experimental/
 
       result = ruby_exe('case 0; in a; end', options: '-W:no-experimental', args: '2>&1')

spec/ruby/core/warning/element_set_spec.rb

@@ -8,8 +8,8 @@ ruby_version_is '2.7' do
     end
 
     it "emits and suppresses warnings for :experimental" do
-      ruby_exe('Warning[:experimental] = true; eval("case 0; in a; end")', args: "2>&1").should =~ /is experimental/
-      ruby_exe('Warning[:experimental] = false; eval("case 0; in a; end")', args: "2>&1").should == ""
+      ruby_exe('Warning[:experimental] = true; eval("1 => a")', args: "2>&1").should =~ /is experimental/
+      ruby_exe('Warning[:experimental] = false; eval("1 => a")', args: "2>&1").should == ""
     end
 
     it "raises for unknown category" do

spec/ruby/language/pattern_matching_spec.rb

@@ -41,11 +41,9 @@ ruby_version_is "2.7" do
     it "warns about pattern matching is experimental feature" do
       -> {
         eval <<~RUBY
-          case 0
-            in 0
-          end
+          1 => a
         RUBY
-      }.should complain(/warning: Pattern matching is experimental, and the behavior may change in future versions of Ruby!/)
+      }.should complain(/warning: One-line pattern matching is experimental, and the behavior may change in future versions of Ruby!/)
     end
 
     it "binds variables" do