[ruby/irb] Fix Reline's test failure running with `make test-all

TESTS='reline irb'`
(https://github.com/ruby/irb/pull/722)

* Specify TestInputMethod in test to avoid RelineInputMethod to be used

* Reset Reline in teardown to avoid test failure of `make test-all TESTS="irb reline"`

https://github.com/ruby/irb/commit/5d67967eb1

test/irb/test_context.rb

@@ -91,7 +91,7 @@ module TestIRB
     end
 
     def test_prompt_n_deprecation
-      irb = IRB::Irb.new(IRB::WorkSpace.new(Object.new))
+      irb = IRB::Irb.new(IRB::WorkSpace.new(Object.new), TestInputMethod.new)
 
       _, err = capture_output do
         irb.context.prompt_n = "foo"

test/irb/test_input_method.rb

@@ -15,6 +15,8 @@ module TestIRB
     def teardown
       IRB.conf.replace(@conf_backup)
       restore_encodings
+      # Reset Reline configuration overrided by RelineInputMethod.
+      Reline.instance_variable_set(:@core, nil)
     end
 
     def test_initialization

test/irb/test_irb.rb

@@ -738,7 +738,7 @@ module TestIRB
       workspace = IRB::WorkSpace.new(TOPLEVEL_BINDING.dup)
 
       IRB.conf[:VERBOSE] = false
-      IRB::Irb.new(workspace)
+      IRB::Irb.new(workspace, TestInputMethod.new)
     end
   end
 end

test/irb/test_ruby_lex.rb

@@ -222,7 +222,7 @@ module TestIRB
       end
 
       IRB.conf[:VERBOSE] = false
-      IRB::Context.new(nil, workspace)
+      IRB::Context.new(nil, workspace, TestInputMethod.new)
     end
 
     def assert_indent_level(lines, expected, local_variables: [])