security: TestRotateCerts fails when pointed to a secondary tenant

[knz]

Found while working on #110001.

Describe the problem

After TestRotateCerts is modify to use .ApplicationLayer() it starts failing as follows when pointed to a secondary tenant:

    certs_rotation_test.go:129: x509: certificate signed by unknown authority (possibly because of "crypto/rsa: verification error" while trying to verify candidate authority certificate "Cockroach CA")

Expected behavior

The behavior should be the same regardless of whether a secondary tenant is used or not.

Epic CRDB-38970

Jira issue: CRDB-31214