V2: Constructing item from geometry with tuple coords

[tylanderson]

Constructing an item from a shapely derived mapping results in validation errors when calling item.validate()

Example:

import shapely
from pystac import Item
import datetime


geom = shapely.from_wkt("POLYGON ((-95.780872 29.517294, -95.783782 29.623358, -96.041791 29.617689, -96.038613 29.511649, -95.780872 29.517294))")
bbox = geom.bounds
geojson = shapely.geometry.mapping(geom)
item = Item(
    id="some_id",
    geometry=geojson,
    bbox=bbox,
    datetime=datetime.datetime.now(),
    properties={},
)
item.validate()

yields an error as coords are expected to validate as lists:

pystac.errors.STACValidationError: {'type': 'Polygon', 'coordinates': (((-95.780872, 29.517294), (-95.783782, 29.623358), (-96.041791, 29.617689), (-96.038613, 29.511649), (-95.780872, 29.517294)),)} is not valid under any of the given schemas...

Surfaced from testing migration to v2 using stactools as test case