Description of problem:

tektonpruner configmap values are getting overrided after upgrade

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Install 1.19.3 operator

1. Enable tektonpruner & update tekton-pruner-default-spec configmap with some values.

global-config: |-    
    enforcedConfigLevel: global
    historyLimit: 8
    failedHistoryLimit: 3
    successfulHistoryLimit: 5  

1. Create few pipelineruns in test namespaces and validate pipelineruns are being pruned with the values set in configmap.

1. Upgrade the operator to 1.20

1. Once the operator upgrade is done, validate the values of tekton-pruner-default-spec configmap.

Actual results:

**

tekton-pruner-default-spec configmap values are getting overrided with default values as below.

global-config: |
    enforcedConfigLevel: global
    ttlSecondsAfterFinished: null
    successfulHistoryLimit: null
    failedHistoryLimit: null
    historyLimit: 100
    namespaces: {} 

Expected results:

The same data before upgrade should be retained in configmap even after upgrade

Reproducibility (Always/Intermittent/Only Once):

Acceptance criteria: 

Definition of Done:

Build Details:

Additional info (Such as Logs, Screenshots, etc):

PFA tektonconfig & configmap files before & after upgrade
[^1.19.3_config_beforeupgrade.yaml] [^1.19.3_config_beforeupgrade.yaml]