Match shebang lines in Vim9 and legacy script.
Mark these as an error if they appear anywhere other than the first line
of a legacy-script file. In Vim9 script these match as normal line
comments rather than an error.
Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
