#3670 codegen: BROKEN_REGEXES override for the @swamp/aws/invoicing InvoiceUnit name lacks the u flag, so it rejects ordinary names

Found while planning #3367.

codegen/shared/util.ts BROKEN_REGEXES maps the CloudFormation pattern for AWS::Invoicing::InvoiceUnit names to ^(?! )[\p{L}\p{N}\p{Z}-_]*(?<! )$ with flags set to the empty string. Without the u flag, \p is an identity escape, so the class matches only the literal characters p, {, L, }, N, Z, - and _.

Generated into model/aws/invoicing/extensions/models/invoice_unit.ts (lines 68 and 105). The module imports fine, so the #3367 compile check does not catch it, but validation is wrong:

• regex.test of Billing returns false (should be true)
• regex.test of pL returns true
• the same source with the u flag accepts Billing

Fix direction: set flags to u on that BROKEN_REGEXES entry, add a util test, regenerate invoicing.