tests: fix unit tests to respect default level names

[ssam18]

Description

This PR fixes unit tests to use default level names instead of being affected by custom or defined in .

Problem

When custom level names are defined in , the unit tests fail:

REQUIRE( spdlog::level::to_string_view(spdlog::level::trace) == "trace" )
with expansion:
  "TRC" == "trace"

Solution

Added and in after to ensure unit tests always use the default level names.

Testing

This change ensures that:

• Unit tests are not affected by user-defined level name customizations
• Tests validate the default behavior of spdlog
• Custom level names in don't break the test suite

Fixes #3466

Thank you to @tt4g for suggesting this fix