[Test] Set explicit heap size in DebPreservationTests to prevent oom-killed failures (#141440) (#141445)

The `@Before` hook for heap sizing runs before installation is assigned,
leading to potential issues with automatic heap sizing.
This change sets the heap size to `1g` explicitly to avoid oom-killed errors during tests.

Author: jozala

qa/packaging/src/test/java/org/elasticsearch/packaging/test/DebPreservationTests.java

@@ -100,6 +100,10 @@ public void test40RestartOnUpgrade() throws Exception {
         installation = installPackage(sh, distribution());
         assertInstalled(distribution());
 
+        // The @Before hook that normally pins heap runs before installation is assigned in this test,
+        // so explicitly set it here to avoid CI oom-killed from auto heap sizing.
+        setHeap("1g");
+
         // Ensure ES is started
         Packages.runElasticsearchStartCommand(sh);
         ServerUtils.waitForElasticsearch(installation);