time: Parse of RFC3339 is incorrect for timezone field

[dsnet]

RFC 3339, section 5.6 specifies that the time-numoffset field must be either a minus or plus sign followed by 2 digits a colon and 2 digits.

However, Parse permits the integer fields having plus and minus signs:

Parse(time.RFC3339, "0000-01-01T00:00:00+-0:+0")

reports nil rather than an error.

[gopherbot]

Change https://go.dev/cl/425038 mentions this issue: time: fix Parse for time zones