Polish PR "Dependency Upgrades" section

[snicoll]

Our PR template for dependency upgrades currently states:

Dependency Upgrades

Please do not open a pull request for a straightforward dependency upgrade (one that
only updates the version property). We have a semi-automated process for such upgrades
that we prefer to use. However, if the upgrade is more involved (such as requiring
changes for removed or deprecated API) your pull request is most welcome.

I think a key element is missing in this text. Rather than focusing on the fact it only updates one line with a version property, we should IMO focus on the fact it is covered by bomr and therefore will be taken care "automatically".

Versions that are handled internally (and aren't covered by bomr) won't be checked automatically and can be outdated unless someone looks at it. Any help we can get to stay current is most welcome.

Maybe we could rephrase the text to mention the content of spring-boot-dependencies since that's what bomr uses?

[snicoll]

We've decided to keep the note as it is and expand bomr coverage, see #21439. We will merge PRs that only update the version property on a case-by-case basis. For internal dependencies, we feel it is less important to upgrade right away unless there is a benefit in doing so.