buildman: Ignore conflicting tags

Tags like Series-version are normally expected to appear once, and with a
unique value. But buildman doesn't actually look at these tags. So ignore
conflicts.

This allows bulidman to build a branch containing multiple patman series.

Reported-by: Steve Rae <srae@broadcom.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/func_test.py b/tools/buildman/func_test.py
index c37f1b6..75eb3a9 100644
--- a/tools/buildman/func_test.py
+++ b/tools/buildman/func_test.py
@@ -79,6 +79,7 @@
     Series-changes: 7
     - Add new patch to fix the 'reverse' bug
 
+    Series-version: 8
 
     Change-Id: I79078f792e8b390b8a1272a8023537821d45feda
     Reported-by: York Sun <yorksun@freescale.com>
@@ -156,6 +157,8 @@
     Series-changes: 9
     - Add new patch to avoid changing the order of tags
 
+    Series-version: 9
+
     Suggested-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
     Change-Id: Ib1518588c1a189ad5c3198aae76f8654aed8d0db
 """]