Injector pod stuck in pending state when upgraded from 0.9.0 to 0.13.0

**Describe the bug**
On 1 Node kubernetes cluster, if you upgrade the vault from 0.9.0 to 0.13.0, the agent injector pod is stuck in pending state

**To Reproduce**
Steps to reproduce the behavior:
1. Install vault 0.9.0 on 1 node Kubernetes cluster
2. Try upgrading to 0.13.0


Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Warning FailedScheduling default-scheduler 0/1 nodes are available: 1 node(s) didn't match pod affinity/anti-affinity.
Warning FailedScheduling default-scheduler 0/1 nodes are available: 1 node(s) didn't match pod affinity/anti-affinity.

Other useful info to include: vault pod logs, `kubectl describe statefulset vault` and `kubectl get statefulset vault -o yaml` output

**Expected behavior**
Should be able to upgrade from 0.9.0 to 0.13.0

**Additional context**
Seems that because of this check in
https://github.com/hashicorp/vault-helm/commit/53f31be2056364ae7a8c35c334f6bca0eac75de3#diff-8377b3e3740a3fcd9f682e5fb55425f2fdbece1791854b9e5013e7f1a5e60e7e

Kubernetes is looking for an node where web hook component is not present. Since this is 1 node, it's always stuck in pending state.

Start by inspecting the affinity/anti-affinity change in commit 53f31be2056364ae7a8c35c334f6bca0eac75de3 and reproduce the 0.9.0-to-0.13.0 upgrade on a single-node Kubernetes cluster. Use the listed kubectl describe and YAML commands to confirm why the injector remains Pending; done means the upgrade succeeds and the injector pod schedules.

Written by the indexing model from the issue text.