springboot Upgrade to Kotlin 1.3.71

Hi,

this PR upgrades to Kotlin 1.3.71.

Cheers, Christoph

Comment From: wilkinsona

Thanks for the PR, @dreis2211. As noted in the pull request template, we prefer to handle this sort of single-line dependency upgrade ourselves. Thanks anyway.

Comment From: dreis2211

I was under the impression that everything that isn't handled by Bomr is still valid, but fair enough. Could the template be made more explicit in that regards that you don't want those PRs at all? Under the same umbrella, eventual testcontainers upgrades are also discouraged although it's not handled by Bomr. Thoughts, @wilkinsona ?