BUG: cadc uploads doesn't close file

The following doesn't close the upload file causing a warning/error. There is a testcase for it in the narrative docs, but apparently the `uploads` kwarg isn't covered by the tests (I'll add a test for it in #2520, albeit with an xfail).

This issue is most likely an upstream pyvo issue, but nevertheless I report here, too.

```
from astroquery.cadc import Cadc
cadc = Cadc()
# save a few observations on a local file
output_file = Path(tmp_path, 'my_observations.xml')
cadc.exec_sync("SELECT TOP 3 observationID FROM caom2.Observation",
output_file=output_file)

# now use them to join with the remote table
results = cadc.exec_sync(
"SELECT o.observationID, intent FROM caom2.Observation o JOIN "
"tap_upload.test_upload tu ON o.observationID=tu.observationID",
uploads={'test_upload': output_file})
```

Start with the CADC upload path exercised by Cadc.exec_sync(..., uploads=...), then compare it with the upload-file handling described by the narrative-doc testcase. Reproduce the warning or error using the example and add coverage alongside the uploads test planned in #2520; done means the uploaded file is closed without the regression and the test passes.

Written by the indexing model from the issue text.