Parse lambda -> ref T as a primitive return form (#7962)

This got lost when I rebased #7911 on top of #7893/#7894's lambda
parsing
rework.

Assisted-by: Claude

toolchain/parse/handle_lambda.cpp

@@ -85,7 +85,7 @@ auto HandleLambdaAfterParams(Context& context) -> void {
     context.PushState(state, StateKind::LambdaBody);
     context.PushState(StateKind::FunctionReturnTypeFinish);
     context.ConsumeAndDiscard();
-    context.PushStateForExpr(PrecedenceGroup::ForType());
+    context.PushState(StateKind::ReturnTypeOrFormExpr);
   } else if (context.PositionIs(Lex::TokenKind::MinusGreaterQuestion)) {
     // Has return form.
     context.PushState(state, StateKind::LambdaBody);