Nada, same error and update now says everything is up to date:
vlad@linux:/var/www/html/admin$ echo release/v4.0 | sudo tee /etc/pihole/ftlbranch
release/v4.0
vlad@linux:/var/www/html/admin$ pihole checkout core release/v4.0
Please note that changing branches severely alters your Pi-hole subsystems
Features that work on the master branch, may not on a development branch
This feature is NOT supported unless a Pi-hole developer explicitly asks!
Have you read and understood this? [y/N] y
[✗] Fetching branches from GitHub - pi-hole/pi-hole: A black hole for Internet advertisements
usage: git ls-remote [--heads] [--tags] [--upload-pack=] [-q | --quiet] [--exit-code] [--get-url] [ [...]]
vlad@linux:/var/www/html/admin$ pihole checkout web release/v4.0
Please note that changing branches severely alters your Pi-hole subsystems
Features that work on the master branch, may not on a development branch
This feature is NOT supported unless a Pi-hole developer explicitly asks!
Have you read and understood this? [y/N] y
[✗] Fetching branches from GitHub - pi-hole/web: Pi-hole Dashboard for stats and more
usage: git ls-remote [--heads] [--tags] [--upload-pack=] [-q | --quiet] [--exit-code] [--get-url] [ [...]]
vlad@linux:/var/www/html/admin$ pihole -up
[i] Checking for updates...
[i] Pi-hole Core: up to date
[i] Web Interface: up to date
[i] FTL: up to date
[✓] Everything is up to date!
The versions in debug are also the same as before:
*** [ DIAGNOSING ]: Core version
[i] Core: v3.3.1 (How do I update Pi-hole?)
[i] Branch: FTLDNS (The pihole Command With Examples)
[i] Commit: v3.3.1-365-g6f2f598
*** [ DIAGNOSING ]: Web version
[i] Web: v3.3 (How do I update Pi-hole?)
[i] Branch: master
[i] Commit: v3.3-0-ge48aa29
*** [ DIAGNOSING ]: FTL version
[✓] FTL: vDev-8e56b61 (How do I update Pi-hole?)