Fix joda migration for week based methods in Painless (elastic#83232)

This change updates the docs to correct suggestions for migrating from 
JodaCompatibleZonedDateTime to ZonedDateTime in Painless for week based year and week of 
week based year.

docs/reference/migration/migrate_8_0/painless-changes.asciidoc

@@ -37,7 +37,8 @@ The following `JodaCompatibleZonedDateTime` methods must be replaced using
 * `getMonthOfYear()` -> `getMonthValue()`
 * `getSecondOfDay()` -> `get(ChronoField.SECOND_OF_DAY)`
 * `getSecondOfMinute()` -> `getSecond()`
-* `getWeekOfWeekyear()` -> `get(DateFormatters.WEEK_FIELDS_ROOT.weekBasedYear())`
+* `getWeekOfWeekyear()` -> `get(IsoFields.WEEK_OF_WEEK_BASED_YEAR)`
+* `getWeekyear()` -> `get(IsoFields.WEEK_BASED_YEAR)`
 * `getYearOfCentury()` -> `get(ChronoField.YEAR_OF_ERA) % 100`
 * `getYearOfEra()` -> `get(ChronoField.YEAR_OF_ERA)`
 * `toString(String)` -> a DateTimeFormatter