bump kataras/iris/v12 to current beta release to resolve CVE-2021-23772

[catkins]

As part of our migration to Sentry, we've been updating our internal Go libraries to use sentry-go. Our Snyk CI pinged us with a couple of CVEs, listed in #438

By bumping iris to the latest beta release, and running go mod tidy (Which cleared out the coreos/etcd dependencies from the go.sum) this should clear out the high severity CVEs.

See: https://app.snyk.io/vuln/SNYK-GOLANG-GITHUBCOMKATARASIRISV12-2325170

[catkins]

cc/ @cweerasooriya

[kamilogorek]

Thanks for the contribution. Would you mind taking look at broken checks?

[stanhu]

I've attempted to do the same in #462.

[kamilogorek]

Fixed in https://github.com/getsentry/sentry-go/pull/462