update docs deploy script: deploy docsets, see #3442

[trichter]

What does this PR do?

Update the deploy script in the obspy repository to reflect changes in the server-side docs deploy code.

Why was it initiated? Any relevant Issues?

See #3442

PR Checklist

• Correct base branch selected? master for new features, maintenance_... for bug fixes
• This PR is not directly related to an existing issue (which has no PR yet).
• While the PR is still work-in-progress, the no_ci label can be added to skip CI builds
• If the PR is making changes to documentation, docs pages can be built automatically.
  Just add the build_docs tag to this PR.
  Docs will be served at docs.obspy.org/pr/{branch_name} (do not use master branch).
  Please post a link to the relevant piece of documentation.
• If all tests including network modules (e.g. clients.fdsn) should be tested for the PR,
  just add the test_network tag to this PR.
• All tests still pass.
• Any new features or fixed regressions are covered via new tests.
• Any new or changed features are fully documented.
• Significant changes have been added to CHANGELOG.txt .
• First time contributors have added your name to CONTRIBUTORS.txt .
• If the changes affect any plotting functions you have checked that the plots
  from all the CI builds look correct. Add the "upload_plots" tag so that plotting
  outputs are attached as artifacts.
• New modules, add the module to CODEOWNERS with your github handle
• Add the yellow ready for review label when you are ready for the PR to be reviewed.