Remove minimumReleaseAge for google/oss-fuzz

[radarhere]

It is unlikely that there will be a whole week where google/oss-fuzz doesn't receive a new commit, meaning that the minimum release age for Renovate is unlikely to ever pass.

Rather than manually triggering the 'github-actions' item in #6604 each month, this PR attempts to remove the minimum release age, just for GitHub Actions.

[hugovk]

Rather than setting it to zero for all actions, can we set it to zero for just google/oss-fuzz?

Then we get extra protection from supply chain attacks, which are becoming more common against GitHub Actions:

https://blog.yossarian.net/2025/11/21/We-should-all-be-using-dependency-cooldowns

Perhaps like:

    "packageRules": [
      {
          "groupName": "github-actions",
          "matchManagers": ["github-actions"],
          "separateMajorMinor": false
      },
      {
          "matchManagers": ["github-actions"],
          "matchPackageNames": ["google/oss-fuzz**"],
          "minimumReleaseAge": "0 days"
      }
    ]

[radarhere]

Why "google/oss-fuzz**" rather than "google/oss-fuzz"?

[hugovk]

"google/oss-fuzz" is better 👍