chore (build): leave dateTime out of locally-built versionInfo

To avoid gradle deciding that engine's build is always stale.

engine/build.gradle

@@ -238,10 +238,18 @@ def createVersionInfoFile = tasks.register("createVersionInfoFile", WritePropert
             jobName: env.JOB_NAME,
             gitBranch: convertGitBranch(env.GIT_BRANCH),
             gitCommit: env.GIT_COMMIT,
-            dateTime: startDateTimeString,
             displayVersion: displayVersion,
             engineVersion: version
     ].findAll { it.value != null })
+    if (env.JOB_NAME != null) {
+        // Only set the dateTime property when there is a Jenkins JOB_NAME.
+        // It is a value we can always get (on Jenkins or otherwise) but we don't want local builds
+        // to invalidate their cache whenever the time changes.
+        // TODO: after upgrading to Gradle 6.8, see if we can have it ignore this property specifically:
+        //     https://docs.gradle.org/current/userguide/more_about_tasks.html#sec:property_file_normalization
+        property("dateTime", startDateTimeString)
+    }
+
     outputFile = "$buildDir/createVersionInfoFile/versionInfo.properties"
 }