Fix generate-docs workflow breakage when run on PR closure

[oleksandr-pavlyk]

Fix for generate documentation workflow. Only run "Publish docs" step if PR is not being closed.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• If this PR is a work in progress, are you opening the PR as a draft?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/1502/index.html

[coveralls]

coverage: 90.684%. remained the same
when pulling f35f2d0 on fix-gen-docs
into 12cd523 on master.

[github-actions]

Array API standard conformance tests for dpctl=0.15.1dev3=py310h15de555_25 ran successfully.
Passed: 908
Failed: 1
Skipped: 86

[ndgrigorian]

Hopefully this will fix the problem

[github-actions]

Deleted rendered PR docs from intelpython.github.com/dpctl, latest should be updated shortly. 🤞