Add bot branch protection bypass in root-signing-staging (#403)

* Remove unused custom role

This was an attempt to allow a specific user/bot to bypass branch
protections in a repository. Luckily we should not need the role
after all.

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

* Add sigstore-bot to root-signing-staging bypass list

Allow sigstore-bot to bypass required pull requests: this is for the
online signing.

Also remove sigstore-reviewe-bot: it should not be needed.

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

---------

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

github-sync/github-data/sigstore/repositories.yaml

@@ -1470,8 +1470,6 @@ repositories:
         permission: admin
       - username: sigstore-bot
         permission: push
-      - username: sigstore-review-bot
-        permission: push
     teams:
       - name: tuf-root-signing-staging-codeowners
         id: 8790813
@@ -1497,6 +1495,8 @@ repositories:
           - sigstore-bot
         dismissalRestrictions:
           - tuf-root-signing-staging-codeowners
+        pullRequestBypassers:
+          - sigstore-bot
       - pattern: publish
         enforceAdmins: true
         allowsDeletions: false