Fix unexpected error when DifferentMethodParameterKind

[ksss]

I encountered a pattern that was causing unexpected errors, so I have fixed it.
It seems that << takes precedence over ||.
This pattern was occurring with Ripper.tokenize.

https://github.com/ruby/ruby/blob/7816307b30189ec7d71d6ce704a9aebd0395d447/ext/ripper/lib/ripper/lexer.rb#L25

https://github.com/ruby/rbs/blob/abcc97d3c8b024856ba9603a7ef22d422652ff42/stdlib/ripper/0/ripper.rbs#L1097

Repro

$ cat t.rb
class Foo
  def foo(**kw)
  end
end

$ cat t.rbs
class Foo
  def foo: (?a: boolish) -> void
end

$ cat Steepfile
target :app do
  check "t.rb"
  signature "t.rbs"
end

$ steep check
# Type checking files:

......................................................................[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)] Unexpected error: RuntimeError
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   /Users/yuki.kurihara/src/github.com/ksss/steep/lib/steep/ast/types/union.rb:16:in `build'
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   /Users/yuki.kurihara/src/github.com/ksss/steep/lib/steep/type_inference/method_params.rb:467:in `build'
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   /Users/yuki.kurihara/src/github.com/ksss/steep/lib/steep/type_construction.rb:199:in `for_new_method'
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   /Users/yuki.kurihara/src/github.com/ksss/steep/lib/steep/type_construction.rb:278:in `with_method_constr'
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   /Users/yuki.kurihara/src/github.com/ksss/steep/lib/steep/type_construction.rb:942:in `block (2 levels) in synthesize'
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   <internal:kernel>:148:in `yield_self'
[Steep 1.5.3] [typecheck:typecheck@2] [background] [#typecheck_source(path=t.rb)] [#type_check_file(t.rb@app)] [synthesize:(1:1)] [synthesize:(2:3)]   /Users/yuki.kurihara/src/github.com/ksss/steep/lib/steep/type_construction.rb:937:in `block in synthesize'
...(snip)

[soutaro]

Thank you so much! 🙏