Release script doesn't work for v3.6.0 (main branch) releases

[ivanvc]

Bug report criteria

• This bug report is not security related, security issues should be disclosed privately via etcd maintainers.
• This is not a support request or question, support requests or questions should be raised in the etcd discussion forums.
• You have read the etcd bug reporting guidelines.
• Existing open issues along with etcd frequently asked questions have been checked and this is not a duplicate.

What happened?

While working on using gh to automate creating the GitHub releases, I noticed that the release script failed when doing v3.6.0 prereleases.

What did you expect to happen?

It should work but fails because it expects a branch release-3.6 to exist.

How can we reproduce it (as minimally and precisely as possible)?

Running the release script with a v3.6.0 version, i.e.:

$ [email protected]:ivanvc/etcd.git DRY_RUN=true ./scripts/release.sh v3.6.0-alpha.2
DRY_RUN=true
RELEASE_VERSION=vv3.6.0-alpha.2
MINOR_VERSION=v3.6
BRANCH=release-v3.6
[email protected]:ivanvc/etcd.git

Preparing temporary directory: /tmp/etcd-release-v3.6.0-alpha.2
% (cd ../../../../../../tmp/etcd-release-v3.6.0-alpha.2 && 'git' 'clone' '[email protected]:ivanvc/etcd.git' '--branch' 'release-v3.6' '--depth' '1')
stderr: Cloning into 'etcd'...
stderr: warning: Could not find remote branch release-v3.6 to clone.
stderr: fatal: Remote branch release-v3.6 not found in upstream origin

Anything else we need to know?

No response

Etcd version (please run commands below)

N/A

Etcd configuration (command line flags or environment variables)

N/A

Etcd debug information (please run commands below, feel free to obfuscate the IP address or FQDN in the output)

N/A

Relevant log output

No response

[ivanvc]

Link to #13538

[ahrtr]

Thanks @ivanvc for raising this.

We will cut branch release-3.6 at a proper timing after we finish all remaining tasks planned for 3.6. But the release script should also have the ability to release alpha/beta (or RC) versions based on main branch directly.