The current .NET SDK in these tests is EOL, and we've been seeing strange SSL errors transiently.
Update to a supported version and remove cruft in the docker image that was there to install the older version.
TODO: submitting first with the ubuntu 22.04 image test skipped, need to follow-up with a fix and unskip the test
Closes#35955
PiperOrigin-RevId: 610798209
apolcyn