PersonIdent: Preserve the timezone when copying with new time

The PersonIdent(PersonIdent,Date) constructor must create a copy with
the same author/email/timezone but different time.  When we changed
the implementation to the new Instant/ZoneId version, we forgot to
pass the timezone. This made fail some tests downstream.

Pass the timezone when constructing the copy.

Change-Id: Iaa979e6dbaa3c55d4c4d2040068ab8b03163cd4e

org.eclipse.jgit/src/org/eclipse/jgit/lib/PersonIdent.java

@@ -240,7 +240,8 @@ public PersonIdent(PersonIdent pi, Instant when, ZoneId tz) {
 	 */
 	@Deprecated(since = "7.1")
 	public PersonIdent(PersonIdent pi, Date aWhen) {
-		this(pi.getName(), pi.getEmailAddress(), aWhen.toInstant());
+		this(pi.getName(), pi.getEmailAddress(), aWhen.toInstant(),
+				pi.tzOffset);
 	}
 
 	/**