bug#38655: Perl mode: TAB or ; insert unwelcome spaces within string

[積丹尼 Dan Jacobson]

In perl mode try typing

$a="a
b";

You'll instead end up with

$a="a
    b";

upon typing the final ";".

OK, fix by removing the spaces perl-mode wrongly inserted it. Then hit
TAB anywhere on the last line. The wrongful spaces return.
emacs-version "26.3"