Handle malformed subscript expressions (#3064)

Closes #3063

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Co-authored-by: Richard Smith <richard@metafoo.co.uk>

toolchain/parser/parser_handle_statement.cpp

@@ -118,7 +118,9 @@ auto ParserHandleStatementForHeaderIn(ParserContext& context) -> void {
 auto ParserHandleStatementForHeaderFinish(ParserContext& context) -> void {
   auto state = context.PopState();
 
-  context.ConsumeAndAddCloseParen(state, ParseNodeKind::ForHeader);
+  context.ConsumeAndAddCloseSymbol(
+      *(TokenizedBuffer::TokenIterator(state.token) + 1), state,
+      ParseNodeKind::ForHeader);
 
   context.PushState(ParserState::CodeBlock);
 }