Fix RandomData.randomString in tests

Author: AuroraLS3

Plan/common/src/testFixtures/java/utilities/RandomData.java

@@ -60,7 +60,7 @@ public static long randomLong(long rangeStart, long rangeEnd) {
     }
 
     public static String randomString(int size) {
-        return new RandomStringGenerator.Builder().withinRange('a', 'Z').get()
+        return new RandomStringGenerator.Builder().withinRange('A', 'z').get()
                 .generate(size);
     }