Disable ASF Dependabot update PRs

[davidzollo]

Since the bot does not handle the CI errors in the PRs it submits, all PRs raised by the bot were previously closed manually, and it has been found that they can be closed. For reference:
https://github.com/apache/infrastructure-asfyaml?tab=readme-ov-file#depend_alerts

What changed

• add github.dependabot_updates: false to .asf.yaml

Why

• disable ASF-managed Dependabot update PRs for this repository
• keep the change minimal and scoped to repository infrastructure config

Impact

• Dependabot update PRs will stop being opened from the ASF repository configuration
• no code, docs, or workflow files are changed

Validation

• ./mvnw spotless:apply -nsu -T 3C
• ./mvnw -q -DskipTests verify -nsu -T 3C

[DanielLeens]

I pulled the latest branch locally.

Current diff is a single ASF-side configuration change:
.asf.yaml -> github.dependabot_updates: false

That is the right scope for disabling ASF Dependabot update PRs without changing project runtime or build behavior. I do not see a code blocker in the current revision. The remaining item is the pending Build check.