Re-enable BWC tests after backport of changes in values source (#68534)

Relates to #68490

build.gradle

@@ -178,8 +178,8 @@ String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull
  */
 
 if ( BuildParams.inFipsJvm ) {
-  bwc_tests_enabled = false
-  bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/issues/66772"
+  bwc_tests_enabled = true
+  bwc_tests_disabled_issue = ""
 }
 if (bwc_tests_enabled == false) {
   if (bwc_tests_disabled_issue.isEmpty()) {

server/src/main/java/org/elasticsearch/search/aggregations/support/MultiValuesSourceFieldConfig.java

@@ -122,7 +122,7 @@ public class MultiValuesSourceFieldConfig implements Writeable, ToXContentObject
         } else {
             this.filter = null;
         }
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_12_0)) {
             this.userValueTypeHint = in.readOptionalWriteable(ValueType::readFromStream);
             this.format = in.readOptionalString();
         } else {
@@ -173,7 +173,7 @@ public class MultiValuesSourceFieldConfig implements Writeable, ToXContentObject
         if (out.getVersion().onOrAfter(Version.V_7_8_0)) {
             out.writeOptionalNamedWriteable(filter);
         }
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_12_0)) {
             out.writeOptionalWriteable(userValueTypeHint);
             out.writeOptionalString(format);
         }