remove incorrect C++20 check from test/CMakeLists.txt (#2663)

It disables entire branch of tests declaration unconditionally because CXX_STANDARD
is not defined there. But even we use CMAKE_CXX_STANDARD here, these tests should
not be disabled with standard >= C++20.

test/CMakeLists.txt

@@ -137,7 +137,7 @@ endif ()
 
 message(STATUS "FMT_PEDANTIC: ${FMT_PEDANTIC}")
 
-if (FMT_PEDANTIC AND CXX_STANDARD LESS 20)
+if (FMT_PEDANTIC)
   # Test that the library can be compiled with exceptions disabled.
   # -fno-exception is broken in icc: https://github.com/fmtlib/fmt/issues/822.
   if (NOT CMAKE_CXX_COMPILER_ID STREQUAL "Intel")