util-jackson: Don't include fractions of a second in test

Problem

The LocalDateTimeSerdeTest#serialize as text test is highly sensitive
as it tries to match serialized/deserialized LocalDateTime instances
including fractions of a second.

Solution

Remove the fractions of a second from the comparison when testing to
reduce the chance for non-determinism.

JIRA Issues: CSL-11031

Differential Revision: https://phabricator.twitter.biz/D684685

util-jackson/src/test/scala/com/twitter/util/jackson/BUILD

@@ -5,7 +5,6 @@ junit_tests(
         "caseclass/*.scala",
         "serde/*.scala",
     ],
-    tags = ["known-to-fail-jira:CSL-11031"],
     dependencies = [
         "3rdparty/jvm/com/fasterxml/jackson/core:jackson-annotations",
         "3rdparty/jvm/com/fasterxml/jackson/core:jackson-core",

util-jackson/src/test/scala/com/twitter/util/jackson/serde/LocalDateTimeSerdeTest.scala

@@ -73,10 +73,17 @@ class LocalDateTimeSerdeTest extends AnyFunSuite with Matchers {
     val mapper = new JacksonObjectMapper()
     mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
     mapper.registerModule(new JavaTimeModule)
-    val actual = mapper.writeValueAsString(NowUtc)
-    val expected = quote(NowUtc.toString)
-    // occasionally Jackson does not include the last 0 when writing the nano seconds
-    expected.startsWith(actual) should be(true)
+    val actualStr = mapper.writeValueAsString(NowUtc)
+    val actualStrUnquoted =
+      actualStr.substring(1, actualStr.length - 1) // drop beginning and end quotes
+    val actual =
+      actualStrUnquoted.substring(
+        0,
+        actualStrUnquoted.lastIndexOf('.')
+      ) // // drop fractions of second
+    val expectStr = NowUtc.toString
+    val expected = expectStr.substring(0, expectStr.lastIndexOf('.')) // drop fractions of second
+    expected should be(actual)
   }
 
   test("deserialize from text") {