Workaround Opera Mobile 73 compatibility data

Opera Mobile has relaunched for Android using Chromium but the compatibility data still thinks lots of features are unsupported:

```
The es-shims polyfill added the following polyfills:
  Array.prototype.every { "opera_mobile":"73" }
  Array.prototype.indexOf { "opera_mobile":"73" }
  Array.prototype.keys { "opera_mobile":"73" }
  Date.now { "opera_mobile":"73" }
  Function.prototype.name { "opera_mobile":"73" }
  Object.entries { "opera_mobile":"73" }
  String.prototype.split { "opera_mobile":"73" }
  String.prototype.trim { "opera_mobile":"73" }
```

See related issues:

browserslist/browserslist#766
babel/babel#15711

packages/govuk-frontend/.browserslistrc

@@ -3,6 +3,7 @@
 
 [javascripts]
 supports es6-module
+not OperaMobile > 0
 
 [stylesheets]
 > 0.1% in GB and not dead