Fix WanCommandAutoCompletionIntegrationTest: expect leading space in completions

- Updated test expectations to include leading space in option completions
- When buffer ends with space (e.g., 'wan-copy region '), completions
  have a leading space character
- Changed assertions from '--region' to ' --region' to match actual behavior
- This aligns with other completion tests like GfshParserAutoCompletionIntegrationTest

Author: JinwooHwang

geode-wan/src/integrationTest/java/org/apache/geode/cache/wan/internal/cli/commands/WanCommandAutoCompletionIntegrationTest.java

@@ -40,12 +40,13 @@ public void testCompletionOffersMandatoryOptionsInAlphabeticalOrderForWanCopyReg
     // Spring Shell 3.x shows ALL options (both mandatory and optional)
     assertThat(candidate.getCandidates()).hasSize(5);
     // Verify that mandatory options (--region and --sender-id) are present
+    // Note: When buffer ends with space, completions have leading space
     List<String> candidateStrings = candidate.getCandidates().stream()
         .map(c -> c.getValue())
         .collect(Collectors.toList());
-    assertThat(candidateStrings).contains("--region", "--sender-id");
+    assertThat(candidateStrings).contains(" --region", " --sender-id");
     // Also verify optional parameters are present
-    assertThat(candidateStrings).contains("--max-rate", "--batch-size", "--cancel");
+    assertThat(candidateStrings).contains(" --max-rate", " --batch-size", " --cancel");
   }
 
   @Test