Fix webpack license warning (go-gitea#21815)

go-gitea#19999 introduced a indirect dependency with a license that was not on
our allowlist yet which produced this warning during webpack:

````
WARNING in License: citeproc@2.4.62 has disallowed license CPAL-1.0 OR AGPL-1.0
````

I've added both licenses to the allowed list and made it so webpack will
now abort on such license errors so that we don't miss those next time.

Co-authored-by: John Olheiser <john.olheiser@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

webpack.config.js

@@ -229,7 +229,8 @@ export default {
       override: {
         'jquery.are-you-sure@*': {licenseName: 'MIT'},
       },
-      allow: '(Apache-2.0 OR BSD-2-Clause OR BSD-3-Clause OR MIT OR ISC)',
+      emitError: true,
+      allow: '(Apache-2.0 OR BSD-2-Clause OR BSD-3-Clause OR MIT OR ISC OR CPAL-1.0)',
       ignore: [
         'font-awesome',
       ],