Add more required CI to model_transparency.

[mihaimaruseac]

Summary

Add a few more required CI checks for model-transparency repository to make sure we don't accidentaly merge PRs before these get a chance to run (due to slow down in provisioning or due to misconfiguration). We're adding several lint jobs and jobs to test the model signing library on Linux only. The repository has several other CI jobs, but those will not be marked as required.

These are added and tested in
sigstore/model-transparency#283.

Release Note

NONE

Documentation

NONE

[github-actions]

🍹 preview on sigstore-github-sync/sigstore/github-prod

Pulumi report

  Previewing update (sigstore/github-prod)

View Live: https://app.pulumi.com/sigstore/sigstore-github-sync/github-prod/previews/cbace12c-8bd2-434b-afd0-bc734be02b0d

@ Previewing update.....
pulumi:pulumi:Stack: (same)
  [urn=urn:pulumi:github-prod::sigstore-github-sync::pulumi:pulumi:Stack::sigstore-github-sync-github-prod]
  ~ github:index/branchProtection:BranchProtection: (update)
      [id=BPR_kwDOKKk2Ts4DA1PL]
      [urn=urn:pulumi:github-prod::sigstore-github-sync::github:index/branchProtection:BranchProtection::model-transparency-main]
      [provider=urn:pulumi:github-prod::sigstore-github-sync::pulumi:providers:github::default_6_2_3::dfb01c0f-bb2a-45c2-9d92-e6152b5cee06]
    ~ requiredStatusChecks: [
        ~ [0]: {
                ~ contexts: [
                      [0]: "DCO"
                    + [1]: "Lint / Lint whitespace (pull_request)"
                    + [2]: "Lint / Python lint (pull_request)"
                    + [3]: "Lint / Type Check (pull_request)"
                    + [4]: "Run unit tests / Signing with Python 3.11 on Linux (pull_request)"
                    + [5]: "Run unit tests / Signing with Python 3.12 on Linux (pull_request)"
                  ]
              }
      ]
@ Previewing update....
Resources:
  ~ 1 to update
  591 unchanged