#3124 Flaky property test: analyzeExpression dot/bracket agreement fails when the generated model name is a CEL keyword

src/domain/expressions/expression_references_property_test.ts, test 'analyzeExpression: hyphenated dot access and bracket access agree', fails intermittently. fast-check counterexample: name 'in' (seed 2022930549, path 45). model.in.resource.spec.x cannot be dot-accessed because in is a CEL reserved word, so the dot form yields no data target while the test expects [name]. The bracket form is fine. Fix: exclude CEL reserved words (in, true, false, null, and the other reserved identifiers) from the modelName arbitrary used for the dot-access form, or assert dot access only for names that are valid CEL identifiers. Found on main at 5c0c6532 during unrelated work (swamp-club#2676); the test file and src/domain/expressions are unchanged there.