Updated Catch2 git download strategy

Catch2 no longer uses 'master' as the default branch, as CMake tries to
use.

As such, the specific tag 'v2.x' is to be used, which safely follows
Catch2's releases.

Author: StableCoder

prepare_catch.cmake

@@ -69,6 +69,7 @@ function(prepare_catch)
           git_catch
           PREFIX ${CMAKE_BINARY_DIR}/catch2
           GIT_REPOSITORY https://github.com/catchorg/Catch2.git
+          GIT_TAG v2.x
           GIT_SHALLOW 1
           TIMEOUT 10
           UPDATE_COMMAND ${GIT_EXECUTABLE} pull