Allow Fn::GetAZs in Fn::Join values

[0xTaoZ]

Summary

• allow Fn::GetAZs as the second argument to Fn::Join
• add regression coverage for the reported Fn::Join/Fn::GetAZs false positive

Rationale

CloudFormation documents Fn::GetAZs as supported in the list-of-values argument for Fn::Join, and Fn::Select already allows the same array-producing function. Without this, cfn-lint reports E1022 for a valid pattern such as joining all AZs into a comma-delimited string.

Validation

• .venv/bin/python -m pytest test/unit/rules/functions/test_join.py -q
• .venv/bin/python -m pytest test/unit/rules/functions -q
• .venv/bin/ruff check test/unit/rules/functions/test_join.py
• .venv/bin/ruff format --check test/unit/rules/functions/test_join.py
• .venv/bin/python -m json.tool src/cfnlint/data/schemas/other/functions/join.json
• .venv/bin/cfn-lint -r us-east-1 -- /tmp/cfn-join-getazs-XXXX.yaml

Fixes #4674