audio/audacity: Fix build after update devel/rapidjson to 1.1.0.763 (a87c745143f7)

Fails to build in phase configure:
CMake Error at cmake-proxies/cmake-modules/dependencies/rapidjson.cmake:6 (add_library):

add_library cannot create ALIAS target "rapidjson::rapidjson" because
target "rapidjson" is itself an ALIAS.

Call Stack (most recent call first):

cmake-proxies/cmake-modules/AudacityDependencies.cmake:230 (include)
CMakeLists.txt:592 (include)

After upstream commit: https://github.com/Tencent/rapidjson/pull/2193

PR: 288442
Approved by: Jack <xxjack12xx@gmail.com> (maintainer)