meta-microsoft: update Yocto compat for gatesgarth

The next release of Yocto is soon and most of the upstream
layers have switched support strings for it.  Support layer
compat for gatesgarth (current) and dunfell (previous).

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I80575a4151e680446113b21f63caab5730417392
diff --git a/meta-olympus/conf/layer.conf b/meta-olympus/conf/layer.conf
index f510b82..2a58334 100755
--- a/meta-olympus/conf/layer.conf
+++ b/meta-olympus/conf/layer.conf
@@ -9,4 +9,4 @@
 BBFILE_PATTERN_olympus-layer = "^${LAYERDIR}/"
 BBFILE_PRIORITY_olympus-layer = "6"
 
-LAYERSERIES_COMPAT_olympus-layer = "warrior"
+LAYERSERIES_COMPAT_olympus-layer = "dunfell gatesgarth"