[Test] Fix SearchRequestCacheDisablingInterceptorTests (#114828)

The #113501 PR introduced a
change where `:index-name` is no longer considered a valid remote index
name. The valid remote index name has to have a non-empty remote cluster
name, e.g. `my-remote-cluster:index-name`.

This PR changes tests to avoid randomly generating empty remote cluster
names.

Resolves #113659,
#113660

Author: slobodanadamovic

muted-tests.yml

@@ -206,12 +206,6 @@ tests:
 - class: org.elasticsearch.smoketest.MlWithSecurityIT
   method: test {yaml=ml/3rd_party_deployment/Test start and stop multiple deployments}
   issue: https://github.com/elastic/elasticsearch/issues/101458
-- class: org.elasticsearch.xpack.security.authz.interceptor.SearchRequestCacheDisablingInterceptorTests
-  method: testHasRemoteIndices
-  issue: https://github.com/elastic/elasticsearch/issues/113660
-- class: org.elasticsearch.xpack.security.authz.interceptor.SearchRequestCacheDisablingInterceptorTests
-  method: testRequestCacheWillBeDisabledWhenSearchRemoteIndices
-  issue: https://github.com/elastic/elasticsearch/issues/113659
 - class: org.elasticsearch.xpack.esql.qa.mixed.MixedClusterEsqlSpecIT
   method: test {categorize.Categorize ASYNC}
   issue: https://github.com/elastic/elasticsearch/issues/113721

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authz/interceptor/SearchRequestCacheDisablingInterceptorTests.java

@@ -91,7 +91,7 @@ public void testRequestCacheWillBeDisabledWhenSearchRemoteIndices() {
             0,
             3,
             String[]::new,
-            () -> randomAlphaOfLengthBetween(0, 5) + ":" + randomAlphaOfLengthBetween(3, 8)
+            () -> randomAlphaOfLengthBetween(1, 5) + ":" + randomAlphaOfLengthBetween(3, 8)
         );
         final ArrayList<String> allIndices = Arrays.stream(ArrayUtils.concat(localIndices, remoteIndices))
             .collect(Collectors.toCollection(ArrayList::new));
@@ -121,7 +121,7 @@ public void testHasRemoteIndices() {
             0,
             3,
             String[]::new,
-            () -> randomAlphaOfLengthBetween(0, 5) + ":" + randomAlphaOfLengthBetween(3, 8)
+            () -> randomAlphaOfLengthBetween(1, 5) + ":" + randomAlphaOfLengthBetween(3, 8)
         );
         final ArrayList<String> allIndices = Arrays.stream(ArrayUtils.concat(localIndices, remoteIndices))
             .collect(Collectors.toCollection(ArrayList::new));