tests: CAN: change duplicate test name: get_capabilities

In twister, we do not include the ZTEST testsuite as part of the
identifier, something we should start doing especially for tests with
multiple suites. The issue happens with same testcase name in different
suites, where results get messed up.
Work around this for now by making the testcase names unqiue until we
have a better solution twister.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>