Release igraph 2.3.4

[krlmlr]

Hotfix release from branch cran-2.3.4, based on v2.3.3. It fixes the r-devel NOTEs and the BLIS test failure on the CRAN check page, and syncs the workflows with main.

Prepare for release:

• git pull
• Check current CRAN check results
• Polish NEWS
• usethis::use_github_links()
• urlchecker::url_check() (also reported by the release-gate workflow)
• devtools::check(remote = TRUE, manual = TRUE)
• devtools::check_win_devel() (uploaded by the win-builder workflow, results by email)
• Update cran-comments.md
• git push
• allcontributors::add_contributors() to update allcontributors' data in the README.
• Update docs based on the C docs.
• Draft a post for the igraph and cynkra blogs.
• Submit link to that post to R weekly + cynkra's social media platforms.
• Add the link to the blog post to the pkgdown's release menu.
• Announce the release on the igraph forum.

Submit to CRAN:

• usethis::use_version('patch')
• devtools::submit_cran() (or the CRAN submission workflow with confirmation: CONFIRM)
• Approve email

Wait for CRAN...

• Accepted 🎉
• usethis::use_github_release()
• usethis::use_dev_version(push = TRUE)