ci(all-features): correct protoc's semver directive field for renovate

[rami3l]

Clearly renovate wasn't happy about dfc31fe:

{
  currentValue: "34.1",
  datasource: "github-releases",
  depName: "protocolbuffers/protobuf",
  packageName: "protocolbuffers/protobuf",
  replaceString: '# renovate: datasource=github-releases depName=protocolbuffers/protobuf versioning=semver\n          PROTOBUF_VERSION: "34.1"\n',
  skipReason: "invalid-value",
  versioning: "semver",
  warnings: [],
  updates: [],
}

The most possible reason seems to be that semver actually means fully accurate semver and nothing else. Hopefully semver-coerced will make it happy again.

I also took the chance to clarify #4767 (comment).

References:

• Docs page
• GitHub Corpus

[rami3l]

Closed in favor of #4773.