Fix data race in OperatingSystemConfig component

[rfranzke]

How to categorize this PR?

/area usability
/kind bug

What this PR does / why we need it:
When a Shoot specifies eviction settings in .spec.kubernetes.kubelet and has more than one worker pool without any overriding kubelet settings (.spec.provider.workers[].kubernetes.kubelet=nil) then there might be a data race in

gardener/pkg/operation/botanist/component/extensions/operatingsystemconfig/operatingsystemconfig.go

Line 485 in ab23368

setDefaultEvictionMemoryAvailable(kubeletConfigParameters.EvictionHard, kubeletConfigParameters.EvictionSoft, o.values.MachineTypes, worker.Machine.Type)

because the maps part of kubeletConfigParameters were shared.

Example Shoot spec:

kind: Shoot
apiVersion: core.gardener.cloud/v1beta1
spec:
  kubernetes:
    kubelet:
      evictionHard:
        memoryAvailable: 1500Mi
      evictionSoft:
        memoryAvailable: 2Gi
      maxPods: 50
      failSwapOn: true
      kubeReserved:
        cpu: 80m
        memory: 1Gi
        pid: 20k
      imageGCHighThresholdPercent: 50
      imageGCLowThresholdPercent: 40
      serializeImagePulls: true
  provider:
    workers:
      - name: cpu-worker-a
        machine:
          type: m5.2xlarge
        maximum: 2
        minimum: 1
        maxSurge: 1
        maxUnavailable: 0
        volume:
          type: gp2
          size: 50Gi
        zones:
          - eu-central-1a
      - name: cpu-worker-c
        machine:
          type: m5.2xlarge
        maximum: 2
        minimum: 1
        maxSurge: 1
        maxUnavailable: 0
        volume:
          type: gp2
          size: 50Gi
        zones:
          - eu-central-1c

Special notes for your reviewer:
/cc @petersutter @dkistner @ialidzhikov

Release note:

A bug has been fixed causing gardenlet to panic when a `Shoot` with multiple worker pools specifies eviction settings for the kubelet configuration in `.spec.kubernetes.kubelet` while `.spec.provider.workers[].kubernetes.kubelet=nil`.

[dkistner]

/lgtm

[petersutter]

/lgtm

[ialidzhikov]

/lgtm