[ML] Adjust serialisation of inference requests for BWC (#92157)

Adjust serialisation for BWC

build.gradle

@@ -137,9 +137,9 @@ tasks.register("verifyVersions") {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
+boolean bwc_tests_enabled = true
 // place a PR link here when committing bwc changes:
-String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/issues/92153"
+String bwc_tests_disabled_issue = ""
 if (bwc_tests_enabled == false) {
   if (bwc_tests_disabled_issue.isEmpty()) {
     throw new GradleException("bwc_tests_disabled_issue must be set when bwc_tests_enabled == false")

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/InferTrainedModelDeploymentAction.java

@@ -138,7 +138,7 @@ public class InferTrainedModelDeploymentAction extends ActionType<InferTrainedMo
             if (in.getVersion().onOrAfter(Version.V_8_3_0)) {
                 skipQueue = in.readBoolean();
             }
-            if (in.getVersion().onOrAfter(Version.V_8_6_0)) {
+            if (in.getVersion().onOrAfter(Version.V_8_7_0)) {
                 textInput = in.readOptionalString();
             } else {
                 textInput = null;
@@ -214,7 +214,7 @@ public class InferTrainedModelDeploymentAction extends ActionType<InferTrainedMo
             if (out.getVersion().onOrAfter(Version.V_8_3_0)) {
                 out.writeBoolean(skipQueue);
             }
-            if (out.getVersion().onOrAfter(Version.V_8_6_0)) {
+            if (out.getVersion().onOrAfter(Version.V_8_7_0)) {
                 out.writeOptionalString(textInput);
             }
         }