get_bucket fails on CEPH S3 API because it assumes <Content> elements are always last in the XML.

[cboettig]

Please specify whether your issue is about:

• [x] a possible bug
• [ ] a question about package functionality
• [ ] a suggested code or documentation change, improvement to the code, or feature request

If you are reporting (1) a bug or (2) a question about code, please supply:

This code will run forever, because the function fails to increment NextMarker correctly:

d2 <- get_bucket(bucket = "drivers", prefix = "noaa/NOAAGEFS_raw/2022-03-20/00", max = Inf,
                base_url="data.ecoforecast.org", region="")

I will submit a PR to fix this.