Use HEAD of rbs to avoid frequently bumping steep_expectations.yml

Gemfile

@@ -12,7 +12,12 @@ end
 
 group(:development) do
   gem('debug', '~> 1.6.1', require: false)
-  gem('rbs', '~> 2.6.0', require: false)
+  gem(
+    'rbs',
+    # To apply https://github.com/ruby/rbs/pull/1056
+    github: 'ruby/rbs',
+    require: false
+  )
   gem('steep', '~> 1.0.1', require: false)
   gem('benchmark-ips', '~> 2.10.0', require: false)
   gem('stackprof')

steep_expectations.yml

@@ -1,13 +1 @@
----
-- file: lib/ulid.rb
-  diagnostics:
-  - range:
-      start:
-        line: 345
-        character: 12
-      end:
-        line: 345
-        character: 16
-    severity: ERROR
-    message: Type `singleton(::Warning)` does not have method `warn`
-    code: Ruby::NoMethod
+--- []