Make mcompiler-120 IT locale independent

[anilvdl]

Fix #1055 - Make IT mcompiler-120 locale-agnostic

What: Replace the locale-dependent verbatim assertion in src/it/mcompiler-120/verify.groovy with locale-independent keyword checks.

Why: The IT asserts unchecked call to add(E) as a member of the raw type, which is the English javac diagnostic. On non-English locales (e.g. German: "nicht geprüfter Aufruf von add(E) als Mitglied des Raw-Typs List") this assertion fails, making the IT pass only under English.

How: Replace the full English message check with two keyword assertions (add(E) and List) that appear in every locale because they are type/method tokens substituted into the localized template, not translated text. The existing Compilation failure and invalid flag guards are retained. This mirrors the approach already applied to the same IT on master.

No production code is changed. Only the IT verification script is touched.

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