[BUG] Assertion `id' failed. cpp2::using_statement_node::for_namespace

[MarekKnapek]

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Steps to reproduce:

• Get latest cppfront source code.
• Compile cppfront, g++ -std=c++20 cppfront.cpp.
• Run cppfront on this test file:

align_:=using"g"_:

Expected result:

• Compilation success, or nice error message printed.

Actual result:

• a.out: parse.h:2142: bool cpp2::using_statement_node::for_namespace() const: Assertion `id' failed.
• Aborted (core dumped)

Found by fuzzing, https://github.com/hsutter/cppfront/issues/1131.