Update `@sentry/browser` dependency to `v7.8.1`

[plibither8]

We’ve been using a rather old release (almost a year) of the @sentry/browser package (v6.13.2). It’ll be beneficial for us to update it to the latest one (v7.8.1).

Probably good to update to have more reliable tracking, and will also remove the warning alert that’s attached to the Sentry issues we see.

[sourcegraph-bot-2]

Heads up @taylorsperry @jasongornall - the "team/frontend-platform" label was applied to this issue.