Compilation errors in case TCB_SPAN_NAMESPACE_NAME is redefined into anything different from "tcb"

[semen-nazarenko83]

Since all tests are using hardcoded namespace "tcb" instead of TCB_SPAN_NAMESPACE_NAME macro and tests are included unconditionally - compilation fails with errors like:
[build] /build/Target/_deps/tcb-span-src/test/test_contract_checking.cpp:10:7: error: 'tcb' has not been declared
[build] 10 | using tcb::make_span;