test: Upgrade Karma to fork with additional fixes (#6639)

The only fix right now is a minor one:

  joeyparrish/karma@d98765e

With the message:

> fix: Fix message event exception
>
> Message events may not have an origin, and they may not have an
> originalEvent field.  This happens in particular when loading Karma
> and the Chromecast SDK on a Chromecast.  An event arrives from the
> platform with neither of these properties.
>
> This fixes the error by checking for originalEvent before accessing
> a property of it.

To see a diff of all current fixes at any time, see:

  karma-runner/karma@master...joeyparrish:karma:shaka-fixes

package.json

@@ -39,7 +39,7 @@
     "jimp": "^0.16.1",
     "js-yaml": "^4.1.0",
     "jsdoc": "github:joeyparrish/jsdoc#2ca85bb6",
-    "karma": "^6.4.3",
+    "karma": "github:joeyparrish/karma#shaka-fixes",
     "karma-coverage": "^2.2.0",
     "karma-jasmine": "^4.0.1",
     "karma-jasmine-ajax": "^0.1.13",