Tests: require newer catch2 version when using c++20, get latest catc…

…h2 v3 version for internal

tests/unittests/CMakeLists.txt

@@ -1,8 +1,13 @@
+if(CMAKE_CXX_STANDARD GREATER_EQUAL 20)
+  set(CATCH2_MIN_VERSION 3.4)
+else()
+  set(CATCH2_MIN_VERSION 3.1)
+endif()
 if(USE_EXTERNAL_CATCH2)
   if (USE_EXTERNAL_CATCH2 STREQUAL AUTO)
-    find_package(Catch2 3.1)
+    find_package(Catch2 ${CATCH2_MIN_VERSION})
   else()
-    find_package(Catch2 3.1 REQUIRED)
+    find_package(Catch2 ${CATCH2_MIN_VERSION} REQUIRED)
   endif()
 endif()
 
@@ -16,7 +21,7 @@ if(NOT Catch2_FOUND)
   FetchContent_Declare(
     Catch2
     GIT_REPOSITORY https://github.com/catchorg/Catch2.git
-    GIT_TAG        v3.1.0
+    GIT_TAG        v3.4.0
     )
   FetchContent_MakeAvailable(Catch2)
   set(CMAKE_MODULE_PATH ${Catch2_SOURCE_DIR}/extras ${CMAKE_MODULE_PATH})