Release inlabru 2.9.0

[finnlindgren]

Prepare for release:

• [x] Update version and make release branch
• [x] Check current CRAN check results
• [x] Check if any deprecation processes should be advanced, as described in Gradual deprecation
• [x] Polish NEWS
• [x] urlchecker::url_check()
• [x] devtools::build_readme()
• [x] devtools::check(remote = TRUE, manual = TRUE)
• [x] devtools::check_mac_release()
• [x] devtools::check_win_devel()
• [x] revdepcheck::revdep_check(num_workers = 4)
• [x] Update cran-comments.md
• [x] git flow release publish 2.9.0
• [x] Check github check results

Submit to CRAN:

• [x] devtools::submit_cran()
• [x] Approve email

Wait for CRAN...

• [x] Accepted :tada:
• [x] Finish release branch
• [x] usethis::use_github_release() from stable branch
• [x] If not already done on devel branch, usethis::use_dev_version(push = TRUE)
• [x] Post on Mastodon