Update specs_polkadot-sdk.yaml with Low Latency topic label

[ezusthold-tpm]

Add new topic label "T20-low-latency" for issues and PRs related to Low Latency 2026 work.

[bkchr]

You can just assign these prs/issues to a project and filter for the project? You don't need labels for this.

[ezusthold-tpm]

You can just assign these prs/issues to a project and filter for the project? You don't need labels for this.

I'm already using a project in github, the use case for this label is to enable automatic sync with Asana via Unito. Unfortunately Unito can't pull in issues/PRs from a github project. It can use labels (preferred), certain patterns in title or description (not preferred - I'm planning to track various issues, not just ones generated by our team), some other parameters of the issue but all inferior to labels sadly.
Manually sync Asana with github would be recipe for failure.
Yesterday we had a conversation with Joyce, she pointed out the topic labels as a possible solution.
Based on the existing labels (eg T16-async-backing) I considered low latency a worthy topic.

[bkchr]

I'm already using a project in github, the use case for this label is to enable automatic sync with Asana via Unito.

🤮🤮🤮

Good that we double all the work, but not my problem :P