Speculative pr-preview fix

[gabrielsanbrito]

In tobie/pr-preview#172, spec-generator migrated from using the api.csswg.org/bikeshed service to the w3.org/publications/spec-generator for generating Bikeshed documents. The HTTP APIs very similar but not the same. The Web Audio CI relies on setting the force param to 1, which is not part of the API surface of the new service.

The same functionality can be achieved in the new service by setting the die-on parameter to "nothing". More info here.

Manually validated by:

1. pr-preview fails in OfflineAudioContext Incremental Rendering #2675
2. The generated URL is https://www.w3.org/publications/spec-generator/?type=bikeshed-spec&output=html&url=https%3A%2F%2Fraw.githubusercontent.com%2Fgabrielsanbrito%2Fweb-audio-api%2F857f48a208522456fd05522a02424b73ce858e7b%2Findex.bs&force=1&md-warning=not%20ready
3. If we switch "force=1" for "die-on=nothing" it works: https://www.w3.org/publications/spec-generator/?type=bikeshed-spec&output=html&url=https%3A%2F%2Fraw.githubusercontent.com%2Fgabrielsanbrito%2Fweb-audio-api%2F857f48a208522456fd05522a02424b73ce858e7b%2Findex.bs&die-on=nothing&md-warning=not%20ready

[mjwilson-google]

Looks good to me, thank you!