rrule value migrated with parse_dates are incompatible with the form widget

Problem/Motivation

Dates migrated with parse_dates are incompatible with the form widget causing there to be no default value "repeat-end-date" element.

Steps to reproduce

Migrate an event with a migration like this:

id: school_calendars
label: School Calendars
migration_group: calendar
migration_tags:
  - node
source:
  plugin: embedded_data
  data_rows:
    -
      title: "My Event"
      time:
        -
          value: "20240412T000000"
          value2: "20240415T000000"
  ids:
    title:
      type: string
process:
  type:
    plugin: default_value
    default_value: event
  title: title
  field_when:
    - plugin: single_value
      source: time
    - plugin: parse_dates
      entity_type: node
      bundle: event
destination:
  plugin: 'entity:node'

Then go to the edit form for the new node and see that "repeat-end-date" has no default value.

Proposed resolution

I noticed that the migrated dates were formatted like this:
Limit: UNTIL=20240414T200000Z
Rule: RRULE:FREQ=DAILY;INTERVAL=1;UNTIL=20240414T200000Z

Where dates entered through the UI were formatted like this:
Limit: UNTIL=UNTIL=2024-12-17
Rule: RULE:FREQ=DAILY;UNTIL=2024-12-17T235959

So i think we just need to look at the parse_dates processor and double check the date formats.

Remaining tasks

User interface changes

API changes

Data model changes