Update min_sdk_version used in testNoUpdatableJarsInBootImage

Updatable apexes should set a min_sdk_version that is not current. This
enforcement does not exist today, but will soon be added to the build
system. In preparation for that, cleanup the min_sdk_version property
used in this unit test.

Test: go test ./apex
Bug: 221087384
Change-Id: I8a163595f85cb0f8dabccc3321ef210215675714