Fail in beforeCommit on all other terms (#94833)

Today `beforeCommit()` would succeed in production if the current term
decreases. This shouldn't happen for sure, but if it does it would be
safer to fail. This commit adjusts the condition so that we only proceed
with the commit if the term is exactly correct.

Author: DaveCTurner

server/src/test/java/org/elasticsearch/cluster/coordination/AtomicRegisterCoordinatorTests.java

@@ -514,7 +514,10 @@ public boolean isInvalidReconfiguration(
         public void beforeCommit(long term, long version, ActionListener<Void> listener) {
             // TODO: add a test to ensure that this gets called
             final var currentTerm = register.readCurrentTerm();
-            if (currentTerm > term) {
+            if (currentTerm == term) {
+                listener.onResponse(null);
+            } else {
+                assert term < currentTerm : term + " vs " + currentTerm;
                 listener.onFailure(
                     new CoordinationStateRejectedException(
                         Strings.format(
@@ -525,9 +528,6 @@ public void beforeCommit(long term, long version, ActionListener<Void> listener)
                         )
                     )
                 );
-            } else {
-                assert currentTerm == term : currentTerm + " vs " + term;
-                listener.onResponse(null);
             }
         }
     }