Fix MasterService to execute tasks in the context in which the task was originally created.

MasterService used to execute tasks in a completely empty context rather than the original context which was captured when the task was created.

Fixes #108628 (DeprecationHttpIT.testDeprecatedSettingsReturnWarnings)

Author: mosche

muted-tests.yml

@@ -66,9 +66,6 @@ tests:
 - class: org.elasticsearch.xpack.test.rest.XPackRestIT
   method: test {p0=transform/transforms_start_stop/Test start already started transform}
   issue: https://github.com/elastic/elasticsearch/issues/98802
-- class: org.elasticsearch.xpack.deprecation.DeprecationHttpIT
-  method: testDeprecatedSettingsReturnWarnings
-  issue: https://github.com/elastic/elasticsearch/issues/108628
 - class: org.elasticsearch.xpack.shutdown.NodeShutdownIT
   method: testAllocationPreventedForRemoval
   issue: https://github.com/elastic/elasticsearch/issues/116363

server/src/main/java/org/elasticsearch/cluster/service/MasterService.java

@@ -913,7 +913,7 @@ public void onFailure(Exception failure) {
 
         @Override
         public Releasable captureResponseHeaders() {
-            final var storedContext = threadContext.newStoredContext();
+            final var storedContext = threadContextSupplier.get();
             return Releasables.wrap(() -> {
                 final var newResponseHeaders = threadContext.getResponseHeaders();
                 if (newResponseHeaders.isEmpty()) {