feat: Public Cloud K8S versions update (cloudnative-pg#9691)

Update the versions used to test the operator on public cloud providers

Signed-off-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Signed-off-by: Jonathan Gonzalez V. <jonathan.gonzalez@enterprisedb.com>
Co-authored-by: public-cloud-k8s-versions-check <public-cloud-k8s-versions-check@users.noreply.github.com>

Author: cnpg-bot

.github/openshift_versions.json

@@ -1,9 +1,8 @@
 [
+  "4.20",
   "4.19",
   "4.18",
   "4.17",
   "4.16",
-  "4.15",
-  "4.14",
-  "4.12"
+  "4.14"
 ]