If sdk_version is empty, by default the library will be built against
the implementation of the framework jars. There are on going project to
automatically repackaging flag libraries in the libray which is built
direactly against the implementation of the framework jars.

This change set the right sdk_version for the testing library.

Bug: 310504781
Test: atest jarjar-rules-generator-test and CI
Change-Id: I24d8dc47f7ed83f0b84c632d24396e2bdf932424