Prior to this commit, the Spring TestContext Framework (TCF) favored a
@Primary transaction manger over one configured via the
TransactionManagementConfigurer API, and this contradicts the behavior
in production Spring applications.
This commit aligns the transaction manger lookup within the TCF so that
a transaction manger configured via the TransactionManagementConfigurer
API is properly favored over a @Primary transaction manager.
Closes gh-24869