false positive E: id.po: unusual-plural-forms 'nplurals=2; plural=n != 1;' => 'nplurals=1; plural=0;'

[jwilk]

Currently we insist on nplurals=1 for Indonesian, but @triyanwn noted in https://github.com/Gnucash/gnucash/pull/787#issuecomment-708096382 that some sentences may require nplurals=2.

[jwilk]

Looking at id.po files that have at least one plural message translated in Debian bullseye, indeed a significant portion of them uses nplurals=2:

• 134 nplurals=1; plural=0;
• 71 nplurals=2; plural=n != 1; (or equivalent)
• 12 nplurals=2; plural=n > 1; (or equivalent)