Draft: Update quay.io/keycloak/keycloak Docker tag to v26

This MR contains the following updates:

Package	Type	Update	Change
quay.io/keycloak/keycloak	final	major	25.0.6 -> 26.2.1
quay.io/keycloak/keycloak	stage	major	25.0.6 -> 26.2.1

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