time: Parse of RFC3339 and RFC3339Nano are not identical for nanoseconds

[dsnet]

The RFC3339 format implicitly supports parsing of fractional seconds.
Consequently, one would expect that it would behave identically to RFC3339Nano.
However, that is not the case where they differ in behavior for sub-nanosecond digits:

const in = "2021-09-29T16:04:33.0000000000Z"
fmt.Println(time.Parse(time.RFC3339, in))
fmt.Println(time.Parse(time.RFC3339Nano, in))

prints:

2021-09-29 16:04:33 +0000 UTC <nil>
0001-01-01 00:00:00 +0000 UTC parsing time "2021-09-29T16:04:33.0000000000Z" as "2006-01-02T15:04:05.999999999Z07:00": cannot parse "0Z" as "Z07:00"

I expect it to print identical results.

[gopherbot]

Change https://go.dev/cl/425037 mentions this issue: time: fix Parse to ignore extra sub-nanosecond digits