local is undefined in ksh93, but not flagged.

For bugs with existing features

• Related to Rule SC3043
• My shellcheck version: Online
• The rule's wiki page does not already cover this (e.g. https://shellcheck.net/wiki/SC2086)
• I tried on https://www.shellcheck.net/ and verified that this is still a problem on the latest commit

In the Wiki for SC3043, it states that local is supported in ksh, but this is not true of ksh93.

Here's a snippet or screenshot that shows the problem:

#!/bin/ksh93
my_function() {
    local local_var="$1"
    echo "${local_var}"
}
my_function some_string

Here's what shellcheck currently says:

No issues detected!

Here's what I wanted or expected to see:

local is undefined in ksh93

Output from the shell

ksh93: my_function[2]: local: not found