The test disabled the shared `Test Size` Item Attribute. On version-15
`FrappeTestCase` rolls back once per class instead of once per test, so the
flag stayed visible for the rest of `TestItem` and broke the seven tests that
build a variant from that attribute.
Build a dedicated attribute and template instead. Nothing the test writes is
reachable from another test, on either branch, so no cleanup is needed.
c488de8f12