Fix push-argument spec to not depend on RBS param name

CI runs the matrix against RBS 3.10.0 through 4.0.2, where
Array#push's restarg parameter is named differently (e.g. `obj`)
than in the RBS version used locally (`objects`). The parameter
name is an incidental detail of the core RBS declaration, not
something this PR's type-checking logic controls, so match on the
substance of the message instead of the exact name.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LCTZUQv2ijSU5Cqgw4CU1f

Author: apiology

spec/type_checker/levels/strict_spec.rb

@@ -66,8 +66,11 @@ def foo str; end
         y = [1]
         y.push 'two'
       ))
+      # The restarg's parameter name (`objects`, `obj`, etc.) varies
+      # across core RBS versions, so match on the substance of the
+      # message rather than the exact name.
       expect(checker.problems.map(&:message))
-        .to eq(['Wrong argument type for Array#push: objects expected Integer, received String'])
+        .to contain_exactly(a_string_matching(/\AWrong argument type for Array#push: \w+ expected Integer, received String\z/))
     end
 
     it 'handles compatible interfaces with self types on call' do