Bump mediacodec test apex version.

The system version recently bumped to 200000000, which caused failures
in tests, because we aren't allowing downgrades. Bump to 300000000 to
make sure the tests pass again.

Bug: 129093117
Test: atest media_swcodec_e2e_tests
Change-Id: Icc84f4a0f749916aded6746923f0d82b2b9dc473