fix: lock bikeshed to version 5

[sidvishnoi]

See #141 (comment), #141 (comment)

To prevent breakage, we'll release action with locked versions of tools.
For the next v2.12.2 release, use the latest v5 release of bikeshed.
When upgrading to bikeshed v7, we'll release a new version of action (2.13.0, not v3), so that if specs are breaking with latest bikeshed, they can individually update their workflows to use v2.12.2 instead of v2 or v2.13.0. Instead of being forced to update, they've a choice to remain at a previous version.

[sidvishnoi]

@MasterKale

• v2.12.2 locks Bikeshed to v5.x.
• Soon (maybe after New Year, unless people ask for it earlier), there will be v2 ==v2.13.0 release that will upgrade Bikeshed to v7.x.y (locked to specific version, not latest v7).

---

• I'd encourage you to update your workflows to use w3c/spec-prod@v2.12.2 until you're sure your specs are ready for newer Bikeshed major versions.
• For those whose specs aren't broken with Bikeshed v6/v7, they can continue to use w3c/spec-prod@v2 seamlessly.

[sidvishnoi]

@tabatkins FYI.

[tabatkins]

Note that, aside from a single breakage I encountered in the CSSWG repo, the only changes I've seen happening have been new errors finding existing markup problems, so it's good to hit.

But sure, I don't mind you managing this in a conservative fashion.

[MasterKale]

Thank you for the tag @sidvishnoi! This'll definitely help keep CI happy while we (WAWG) promote our current text to Recommendation. Then we can go back into the new working draft and fix the (correctly identified) markup issues flagged by newer versions of bikeshed 🙏