bazel: update `.bazelversion` to latest rolling release
bazel: update `.bazelversion` to latest rolling release

https://github.com/bazelbuild/bazel/releases/tag/6.0.0-pre.20220414.2

As [discussed in Slack][slack], there are a number of disadvantages to
staying on LTS releases.

This can also help unblock Envoy Mobile's iOS releases:
https://github.com/envoyproxy/envoy-mobile/pull/2217

[slack]: https://envoyproxy.slack.com/archives/C7E6C71QB/p1651089150478729

Signed-off-by: JP Simard <0f41a0b3b760b54df703e860e40fef1c388ed2c5@jpsim.com>

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