chore: Let Renovate keep updating spec bumps the webhook handler commits to (#246)

Ignores `flagsmith-engineering[bot]`'s commits on Renovate's branches,
so Renovate keeps rebasing spec bump pull requests after the webhook
handler commits to them.

The handler is going to set the SDK's `tags` in `sdk-spec.yml` on spec
bumps, from the spec's compatibility matrix at the version the bump pins
(Flagsmith/github-webhook-handler#150). Without this, Renovate treats
such a branch as modified and stops updating it.

Part of Flagsmith/sdk-spec#13.

Co-authored-by: flagsmithsmith[bot] <346993984+flagsmithsmith[bot]@users.noreply.github.com>

Author: flagsmithsmith[bot]

renovate.json

@@ -1,5 +1,6 @@
 {
     "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+    "gitIgnoredAuthors": ["216534828+flagsmith-engineering[bot]@users.noreply.github.com"],
     "extends": ["config:recommended", ":semanticCommitScopeDisabled"],
     "ignorePresets": [":semanticPrefixFixDepsChoreOthers"],
     "semanticCommitType": "deps",