Fix Postal Code is optional

[Nef10]

Some countries do not use postal codes, so the field is actually optional

[github-actions]

Coverage after merging postal-code into main

9.25%

Coverage Report

File	Stmts	Funcs	Lines	Uncovered Lines
Sources/RogersBankDownloader
DownloadError.swift	94.12%	100%	93.75%	33
RogersAccount.swift	0%	0%	0%	101–105, 107–111, 137–139, 141–167, 169–171, 173–175, 177–179, 181–205, 207–237, 239–241, 243–274, 276–283
RogersActivity.swift	96.77%	100%	95.83%	240
RogersUser.swift	0%	0%	0%	100–105, 107–135, 38–42, 44–53, 59–61, 63–79, 81–99
URLTaskHelper.swift	0%	0%	0%	10–18, 7–9