Added constant sequence test

Author: tejaswi0910

src/test/java/com/thealgorithms/dynamicprogramming/LongestArithmeticSubsequenceTest.java

@@ -29,6 +29,6 @@ void testGetLongestArithmeticSubsequenceLengthThrowsForNullInput() {
     }
 
     private static Stream<Arguments> provideTestCases() {
-        return Stream.of(Arguments.of(new int[] {3, 6, 9, 12, 15}, 5), Arguments.of(new int[] {1, 7, 10, 13, 14, 19}, 4), Arguments.of(new int[] {1, 2, 3, 4}, 4), Arguments.of(new int[] {}, 0), Arguments.of(new int[] {10}, 1), Arguments.of(new int[] {9, 4, 7, 2, 10}, 3));
+        return Stream.of(Arguments.of(new int[] {3, 6, 9, 12, 15}, 5), Arguments.of(new int[] {1, 7, 10, 13, 14, 19}, 4), Arguments.of(new int[] {1, 2, 3, 4}, 4), Arguments.of(new int[] {}, 0), Arguments.of(new int[] {10}, 1), Arguments.of(new int[] {9, 4, 7, 2, 10}, 3), Arguments.of(new int[] {1, 2, 2, 2, 2, 5}, 4));
     }
 }