test: Replace OPA 1.12.2 with 1.12.3

Author: NickLarsenNZ

tests/test-definition.yaml

@@ -5,12 +5,12 @@ dimensions:
       # To use a custom image, add a comma and the full name after the product version
       # 0.67.1,oci.stackable.tech/sdp/opa:0.67.1-stackable0.0.0-dev
       - 1.8.0
-      - 1.12.2
+      - 1.12.3
   - name: opa-latest
     values:
       # To use a custom image, add a comma and the full name after the product version
       # 0.67.1,oci.stackable.tech/sdp/opa:0.67.1-stackable0.0.0-dev
-      - 1.12.2
+      - 1.12.3
   - name: keycloak
     values:
       - 23.0.1