time: Parse of RFC3339 is incorrect for second field

[dsnet]

RFC 3339, section 5.6 specifies that the time-second field must be two digits wide,
followed by an optional period and one or more digits.

However, Parse permits that field having zero digits and a period and extra digits:

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

reports nil rather than an error.

[gopherbot]

Change https://go.dev/cl/425036 mentions this issue: time: fix Parse for empty seconds