Prohibit keywords for dot access.

[LilithHafner]

I ran into this real-world example:

function throw_default_branch_error(branches, cmd_succeeded)
    branch_detail = if isempty(branches)
        "none of DEFAULT_BRANCH_NAMES found"
    else
        "couldn't decide which of $branches is the default".
    end
    remote_detail = if cmd_succeeded
        "git remote show origin didn't specify the a HEAD branch"
    else
        "remote show origin failed"
    end
    error("""
        Unable to determine the default branch locally ($branch_detail).
        Also unnable to determine the default branch by querying the remote ($remote_detail).
        You can typically bypass this error by specifying the version manually (i.e. pass `-rev=...` to the CLI)
        """)
end

end

julia> throw_default_branch_error([], false)
"none of DEFAULT_BRANCH_NAMES found"

The issue is that (;var"end"=5). end == 5 parses just fine and does not treat end as a keyword. Indeed keywords are accepted after . in all cases that I've checked. It would be a breaking/minor change to fix this. This is present in 1.6 and 1.11.