Fix k8s rootless Docker filesystem permissions (#366)

Without this the deployment fails because the runner can't write to
/data/

Credit to @ccureau for identifying the fix

Relates to: gitea/act_runner#264

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/366
Reviewed-by: techknowlogick <techknowlogick@noreply.gitea.com>
Co-authored-by: Andrew Imeson <andrew@andrewimeson.com>
Co-committed-by: Andrew Imeson <andrew@andrewimeson.com>

examples/kubernetes/rootless-docker.yaml

@@ -41,6 +41,8 @@ spec:
       - name: runner-data
         persistentVolumeClaim:
           claimName: act-runner-vol
+      securityContext:
+        fsGroup: 1000
       containers:
       - name: runner
         image: gitea/act_runner:nightly-dind-rootless