Open3 method signatures do not allow the optional env hash as first argument

[eoinkelly]

Many methods in the Open3 module allow us to optionally pass a Hash as the first positional argument (the hash is used to set the environment for the spawned process) e.g.

stdin, stdout, stderr, wait_thr = Open3.popen3([env,] cmd... [, opts])

The type signatures for these methods currently forbid this e.g.

sorbet-typed/lib/ruby/all/open3.rbi

Lines 3 to 11 in 22dd994

	module Open3
	sig do
	params(
	cmd: T.any(String, T::Array[String]),
	opts: T::Hash[Symbol, T.untyped],
	block: T.proc.params(stdin: IO, stdout: IO, stderr: IO, wait_thr: Thread).void
	).returns([IO, IO, IO, Thread])
	end
	def self.popen3(*cmd, **opts, &block); end

I can "fix" this by changing the type of the cmd from T.any(String, T::Array[String]) to cmd: T.any(String, T::Array[String], T::Hash[String, String]) but that seems wrong to me. Is there a better way to express these method signatures?

I'm happy to attempt a PR for this.