Billing_plan field deprecation - correction start date (#3556)

Co-authored-by: ci.datadog-api-spec <packages@datadoghq.com>

Author: api-clients-generation-pipeline[bot]

.generator/schemas/v1/openapi.yaml

@@ -20236,7 +20236,7 @@ components:
           type: string
         billing_plan:
           deprecated: true
-          description: The billing plan (metadata). (Deprecated from May 2026)
+          description: The billing plan (metadata). (Deprecated from June 2026)
           type: string
         end_date:
           description: Shows the last date of usage.

src/main/java/com/datadog/api/client/v1/model/UsageBillableSummaryHour.java

@@ -116,7 +116,7 @@ public UsageBillableSummaryHour billingPlan(String billingPlan) {
   }
 
   /**
-   * The billing plan (metadata). (Deprecated from May 2026)
+   * The billing plan (metadata). (Deprecated from June 2026)
    *
    * @return billingPlan
    * @deprecated