[ML] Fix DFA source filtering versions and unmute BWC tests (elastic#49725)

Relates elastic#49690

Author: dimitris-athanasiou

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/dataframe/DataFrameAnalyticsSource.java

@@ -77,7 +77,7 @@ public DataFrameAnalyticsSource(String[] index, @Nullable QueryProvider queryPro
     public DataFrameAnalyticsSource(StreamInput in) throws IOException {
         index = in.readStringArray();
         queryProvider = QueryProvider.fromStream(in);
-        if (in.getVersion().onOrAfter(Version.CURRENT)) {
+        if (in.getVersion().onOrAfter(Version.V_7_6_0)) {
             sourceFiltering = in.readOptionalWriteable(FetchSourceContext::new);
         } else {
             sourceFiltering = null;
@@ -95,7 +95,7 @@ public DataFrameAnalyticsSource(DataFrameAnalyticsSource other) {
     public void writeTo(StreamOutput out) throws IOException {
         out.writeStringArray(index);
         queryProvider.writeTo(out);
-        if (out.getVersion().onOrAfter(Version.CURRENT)) {
+        if (out.getVersion().onOrAfter(Version.V_7_6_0)) {
             out.writeOptionalWriteable(sourceFiltering);
         }
     }

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/mixed_cluster/90_ml_data_frame_analytics_crud.yml

@@ -1,8 +1,3 @@
-setup:
-  - skip:
-      version: "all"
-      reason:  "Until backport of https://github.com/elastic/elasticsearch/issues/49690"
-
 ---
 "Get old outlier_detection job":
 

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/90_ml_data_frame_analytics_crud.yml

@@ -1,7 +1,4 @@
 setup:
-  - skip:
-      version: "all"
-      reason:  "Until backport of https://github.com/elastic/elasticsearch/issues/49690"
 
   - do:
       index:

x-pack/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/90_ml_data_frame_analytics_crud.yml

@@ -1,8 +1,3 @@
-setup:
-  - skip:
-      version: "all"
-      reason:  "Until backport of https://github.com/elastic/elasticsearch/issues/49690"
-
 ---
 "Get old cluster outlier_detection job":