Add test for align_params with arity mismatch

Type params validation runs before the alignment, so the arity mismatch
raises GenericParameterMismatchError instead of building a broken
substitution.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TBY8ct4HpkVkZNPdsNHEDE

Author: claude

test/rbs/environment_test.rb

@@ -368,6 +368,9 @@ module Foo[A, B]
 
 module Foo[X, Y]
 end
+
+module Foo[X]
+end
 EOF
 
     Environment::ModuleEntry.new(type_name("::Foo")).tap do |entry|
@@ -383,6 +386,16 @@ module Foo[X, Y]
         assert_equal RBS::Types::Variable.new(name: :B, location: nil), subst[RBS::Types::Variable.new(name: :Y, location: nil)]
       end
     end
+
+    Environment::ModuleEntry.new(type_name("::Foo")).tap do |entry|
+      entry << [nil, decls[0]]
+      entry << [nil, decls[2]]
+
+      # The type params validation runs before the alignment, so the arity mismatch is detected first
+      assert_raises RBS::GenericParameterMismatchError do
+        entry.align_params(decls[2])
+      end
+    end
   end
 
   def test_absolute_type