Vendor `gardener@v1.71.2` and Adapt extension for workerless `Shoot`

[acumino]

How to categorize this PR?

/area open-source /kind enhancement

What this PR does / why we need it:

• Vendor gardener v1.71.0
• Set workerlessSupported to true for type shoot-cert-service

Which issue(s) this PR fixes: Part of https://github.com/gardener/gardener/issues/7635

Special notes for your reviewer:

Release note:

The following dependency is updated:
- github.com/gardener/gardener: v1.65.3 -> v1.71.0
- k8s.io/* : v0.26.1 -> v0.26.3
- sigs.k8s.io/controller-runtime: v0.14.4-> v0.14.6

The `shoot-cert-service` extension now supports workerless `Shoot`s.

[acumino]

/test

[acumino]

/invite @MartinWeindel