Repeated stack traces from `pbench-unpack-tarballs`, "Destination path already exists"

[portante]

It appears that pbench-unpack-tarballs can get itself into a state where an unpacked tar ball is already unpacked, and every minute it throws a stack trace.

2023-01-16T11:55:01.781274 ERROR 248010 139804971293568 pbench-unpack-tarballs unpack_tarballs unpack_tarballs 108 -- Error processing pbench-user-benchmark__2023.01.04T20.50.30.tar.xz
Traceback (most recent call last):
  File "/opt/pbench-server/lib/pbench/server/cache_manager.py", line 358, in do_move
    shutil.move(src, dest)
  File "/usr/lib64/python3.9/shutil.py", line 823, in move
    raise Error("Destination path '%s' already exists" % real_dst)
shutil.Error: Destination path '/srv/pbench/public_html/incoming/6b9f18a77c40/pbench-user-benchmark__2023.01.04T20.50.30/pbench-user-benchmark__2023.01.04T20.50.30' already exists

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/pbench-server/lib/pbench/server/unpack_tarballs.py", line 101, in unpack_tarballs
    self.unpack(tarball)
  File "/opt/pbench-server/lib/pbench/server/unpack_tarballs.py", line 47, in unpack
    self.cache_manager.unpack(tb.dataset.resource_id)
  File "/opt/pbench-server/lib/pbench/server/cache_manager.py", line 909, in unpack
    tarball.controller.unpack(dataset_id)
  File "/opt/pbench-server/lib/pbench/server/cache_manager.py", line 567, in unpack
    tarball.unpack(self.incoming, self.results)
  File "/opt/pbench-server/lib/pbench/server/cache_manager.py", line 392, in unpack
    self.do_move(unpacked_temp / self.name, unpacked, self.tarball_path)
  File "/opt/pbench-server/lib/pbench/server/cache_manager.py", line 360, in do_move
    raise TarballUnpackError(
pbench.server.cache_manager.TarballUnpackError: An error occurred while unpacking /srv/pbench/archive/fs-version-001/6b9f18a77c40/pbench-user-benchmark__2023.01.04T20.50.30.tar.xz: Error moving '/srv/pbench/public_html/incoming/6b9f18a77c40/pbench-user-benchmark__2023.01.04T20.50.30.unpack/pbench-user-benchmark__2023.01.04T20.50.30' to '/srv/pbench/public_html/incoming/6b9f18a77c40/pbench-user-benchmark__2023.01.04T20.50.30': Destination path '/srv/pbench/public_html/incoming/6b9f18a77c40/pbench-user-benchmark__2023.01.04T20.50.30/pbench-user-benchmark__2023.01.04T20.50.30' already exists