[lldb] Fix stdcpp type summary mistakenly marked as regex (NFC) (#66949)

`std::basic_string<char>` is not a regex, and treating it as such could
unintentionally
cause a formatter to substring match a template type parameter, for
example:
`std::vector<std::basic_string<char>>`.

Differential Revision: https://reviews.llvm.org/D158663