ANNOUNCE: Please observe subject format [J/N/O:linux-kvm], other formats deprecated

[Agathe Porte]

Hello,

We recently merged this PR for kernel-docs:stable-patch-format.rst
https://github.com/canonical/kernel-docs/pull/48

It makes the rules about the subject lines on this ML more strict:
https://canonical-kernel-docs.readthedocs-hosted.com/en/latest/reference/stable-patch-format/#subject-line

>From now on the only valid format for SRU series target is the
following:

> [J/N/O:linux-kvm]

(This is an example)

Historically, the rule has been somewhat flexible, and various styles
have been permitted:

> [SRU][B,F][PATCH 1/1] KVM: fix overflow of zero page refcount with ksm running
> [SRU][B][F][PATCH 1/1] KVM: fix overflow of zero page refcount with ksm running
> [SRU][Bionic,Focal][PATCH 1/1] KVM: fix overflow of zero page refcount with ksm running
> [SRU][Bionic/Focal][PATCH 1/1] KVM: fix overflow of zero page refcount with ksm running
> [SRU][Bionic][Focal][PATCH 1/1] KVM: fix overflow of zero page refcount with ksm running

These formats are deprecated. Such submissions will be considered faulty
in the near future and probably get ignored by automatic tooling.

Thanks.