Fix unittest for local timezones

The Unit Test (gramps.plugins.test.exports_test.test_ged) is broken when the
OS is not in UTC time zone. This patch improves the test filter to ignore
dates and times belonging to the last change (CHAN).

Also, the buffer for the previous tokens had to be increased.

Fixes #12902.

gramps/plugins/test/exports_test.py

@@ -114,7 +114,7 @@ def get_prev_token(back):
 
     # pylint: disable=unsubscriptable-object
     if line.startswith("@@"):
-        gedfilt.prev = [None] * 8
+        gedfilt.prev = [None] * 16
         gedfilt.indx = 0
         return False
     retval = True
@@ -125,21 +125,27 @@ def get_prev_token(back):
     if diftyp == " ":
         # save the line for later if needed to figure out the data element
         gedfilt.prev[gedfilt.indx] = token, level, line
-        gedfilt.indx = (gedfilt.indx + 1) % 8
+        gedfilt.indx = (gedfilt.indx + 1) % 16
         retval = False
     elif diftyp == "-":
         # save the line for later if needed to figure out the data element
         gedfilt.prev[gedfilt.indx] = token, level, line
-        gedfilt.indx = (gedfilt.indx + 1) % 8
+        gedfilt.indx = (gedfilt.indx + 1) % 16
         if token == "VERS" and get_prev_token(2) == "SOUR":
             # we must have a header with Gramps version
             retval = False
         elif token == "DATE" and get_prev_token(2) == "NAME":
             # we must have a header with file date
             retval = False
+        elif token == "DATE" and get_prev_token(2) == "CHAN\n":
+            # probably have a timestamp of last change
+            retval = False
         elif token == "TIME" and get_prev_token(2) == "DATE":
             # probably have a header with file time
             retval = False
+        elif token == "TIME" and get_prev_token(2) == "CHAN\n":
+            # probably have a timestamp of last change
+            retval = False
         elif token == "FILE" and line.endswith(".ged\n"):
             # probably have a header with file name
             retval = False
@@ -158,6 +164,11 @@ def get_prev_token(back):
         ):
             # we must have a header with file date
             retval = False
+        elif token == "DATE" and (
+            get_prev_token(3) == "CHAN\n" or get_prev_token(4) == "CHAN\n"
+        ):
+            # probably have a timestamp of last change
+            retval = False
         elif token == "TIME" and (
             get_prev_token(2) == "DATE" or get_prev_token(3) == "DATE"
         ):