Fix patch branch comparison

[hugovk]

This came up during My First Patch Release (3.14.1):

✅  Checking Git repository is clean
It doesn't look like you're on the correct branch.
Are you sure you want to tag? (y/n) >

I was on branch-3.14.1, which was correct.

It comes from this code, which only runs for patch > 0:

    # make sure we're on the correct branch
    if tag.patch > 0:
        if (
            get_output(["git", "name-rev", "--name-only", "HEAD"]).strip().decode()
            != tag.basic_version
        ):
            print("It doesn't look like you're on the correct branch.")

No, they don't match, because tag.basic_version is 3.14 but git name-rev --name-only HEAD is branch-3.14.1 because the script has just created that branch.

So change it to compare the branch name with f"branch-{tag}" (branch-3.14.1) instead.