.get_absolute_href() wrongly rewrites /vsi urls

## Issue After updating to pystac 1.14.2 absolute asset hrefs such as GDAL /vsi... get wrongly rewritten ### Example: ```python import datetime as dt from shapely import box from pystac import Asset, Collection, Item col = Collection.from_file("https://stac.dataspace.copernicus.eu/v1/collections/cop-dem-glo-30-dged-cog") item = Item(id="test", datetime=dt.datetime(2020,1,1, tzinfo=dt.timezone.utc), bbox=[10,10,11,11], geometry=box(10,10,11,11), properties={}, assets={"data": Asset(href="/vsigs/bucket/prefix/file.tif")}) col.add_item(item) print(item.assets["data"].href) print(item.assets["data"].get_absolute_href()) ``` ### Prints ``` /vsigs/bucket/prefix/file.tif https://stac.dataspace.copernicus.eu/vsigs/bucket/prefix/file.tif ``` ## Expected behavior Absolute file path starting with a `/` should stay as is when calling `get_absolute_href()` on an asset.