test(#108): cover nested @ with phi-is-not-first

[VasilevNStas]

fix #108

What

A regression test for the exact case from the issue: a nested @
attribute (bar > @ inside a child object) is covered by the existing
names/phi-is-not-first lint.

Why

The parser lifts a nested @ up to the top level of its parent, where it
becomes a φ sibling that is never first (the container always precedes
it). The phi-is-not-first lint checks exactly that, so the confusing
code from the issue is already reported. The claim was made in
#108 (comment),
but was not backed by a test. This pack locks the behavior in, so a future
regression in the lint or in the parser would be caught by CI.

Changes

• src/test/resources/org/eolang/lints/packs/single/phi-is-not-first/catches-nested-at.yaml — the new regression pack

Both mvn test (591 tests) and mvn clean install -Pqulice pass.

[VasilevNStas]

@volodya-lombrozo plz review