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Was this something which used to work for you, and then stopped?

I am trying to get this working for the first time

Describe the problem

I want to apply allowedVersions to nvm:

    {
      "matchPackageNames": [
        "satantime/puppeteer-node",
        "@types/node",
        "nodejs/node"
      ],
      "allowedVersions": "/^\\d*[02468]\\./",
      "branchTopic": "node-{{{newMajor}}}{{#if separateMinorPatch}}{{#if isPatch}}.{{{newMinor}}}{{/if}}{{/if}}.x{{#if isLockfileUpdate}}-lockfile{{/if}}"
    }

However, all PRs don't have .nvmrc at all, despite nodejs/node.
Job logs show:

      {
        "deps": [
          {
            "depName": "node",
            "currentValue": "18.18.2",
            "datasource": "github-tags",
            "packageName": "nodejs/node",
            "updates": [],
            "versioning": "node",
            "warnings": [],
            "sourceUrl": "https://github.com/nodejs/node",
            "registryUrl": "https://github.com",
            "currentVersion": "18.18.2",
            "isSingleVersion": true,
            "fixedVersion": "18.18.2"
          }
        ],
        "packageFile": ".nvmrc"
      },

It looks obvious that based on currentValue, currentVersion, fixedVersion it should be updated to 20.x.x, but nothing happens.

The issue here is that nvm version includes v, and the right allowedVersions is ^v?\\d*[02468]\\./", but it's impossible to guess about this.

I would propose to apply allowedVersions to the parsed (extracted) version, so I wouldn't worry whether v should be or shouldn't be here.

Relevant debug logs

      {
        "deps": [
          {
            "depName": "node",
            "currentValue": "18.18.2",
            "datasource": "github-tags",
            "packageName": "nodejs/node",
            "updates": [],
            "versioning": "node",
            "warnings": [],
            "sourceUrl": "https://github.com/nodejs/node",
            "registryUrl": "https://github.com",
            "currentVersion": "18.18.2",
            "isSingleVersion": true,
            "fixedVersion": "18.18.2"
          }
        ],
        "packageFile": ".nvmrc"
      },

Have you created a minimal reproduction repository?

I have explained in the description why a minimal reproduction is impossible