glibc: apparmor userns mitigation breaks test suite (again)

The latest policy on apparmor vs userns isn't to reject the namespace creation outright but rather to deny all capabilities within that namespace.

That breaks the glibc testsuite, again, because our patch only takes the former policy into account, and so all tests that use test-container or some ad-hoc code to create a userns will fail any time they try to do something interesting, e.g.:

2722s FAIL: elf/tst-glibc-hwcaps-cache
2722s original exit status 1
2722s error: test-container.c:1136: could not create a private mount namespace
2722s