fix(persian): correct the Persian name of Sunday - #392

The Persian name for Sunday in FaWeeks is misspelled:

FaWeeks = []string{"نجشنبه", "دوشنبه", ...}

Index 0 is Sunday (EnWeeks[0] is "Yekshanbeh", and lang/fa.json spells it یکشنبه), so ToWeekString(FaLocale) returned نجشنبه for Sundays. TestPersian_ToWeekString asserted the misspelled value, so I changed that assertion to یکشنبه and corrected the entry.

I couldn't run Go locally, so I ran the suite on a fork:

• Test only, without the fix: test fails on ubuntu at persian_unit_test.go:214 with expected: "یکشنبه" and actual : "نجشنبه". The windows and macOS jobs of that run were cancelled after that failure.
• Test with the fix: test passes on ubuntu and windows. The macOS job was cancelled before any step ran, so it gave no result.

The commit in this PR is the squashed form of the fix branch (identical tree).