Update versions for indexing pressure backport (#59472)

This commit updates the node stats version constants to reflect the fact
that index pressure stats were backported to 7.9. It also reenables BWC
tests.

build.gradle

@@ -174,8 +174,8 @@ tasks.register("verifyVersions") {
  * after the backport of the backcompat code is complete.
  */
 
-boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/59467" /* place a PR link here when committing bwc changes */
+boolean bwc_tests_enabled = true
+final String bwc_tests_disabled_issue = "" /* place a PR link here when committing bwc changes */
 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")

rest-api-spec/src/main/resources/rest-api-spec/test/nodes.stats/50_indexing_pressure.yml

@@ -1,8 +1,8 @@
 ---
 "Indexing pressure stats":
   - skip:
-      version: " - 7.99.99"
-      reason: "indexing_pressure not in prior versions"
+      version: " - 7.8.99"
+      reason: "indexing_pressure was added in 7.9"
       features: [arbitrary_key]
 
   - do:

server/src/main/java/org/elasticsearch/action/admin/cluster/node/stats/NodeStats.java

@@ -113,8 +113,7 @@ public NodeStats(StreamInput in) throws IOException {
         discoveryStats = in.readOptionalWriteable(DiscoveryStats::new);
         ingestStats = in.readOptionalWriteable(IngestStats::new);
         adaptiveSelectionStats = in.readOptionalWriteable(AdaptiveSelectionStats::new);
-        // TODO: Change after backport
-        if (in.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_7_9_0)) {
             indexingPressureStats = in.readOptionalWriteable(IndexingPressureStats::new);
         } else {
             indexingPressureStats = null;
@@ -267,8 +266,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalWriteable(discoveryStats);
         out.writeOptionalWriteable(ingestStats);
         out.writeOptionalWriteable(adaptiveSelectionStats);
-        // TODO: Change after backport
-        if (out.getVersion().onOrAfter(Version.V_8_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_7_9_0)) {
             out.writeOptionalWriteable(indexingPressureStats);
         }
     }