CI: switch to $BRANCH orchestra too

.orchestra/ci/ci.sh

@@ -36,6 +36,9 @@ EOF
 fi
 set -x
 
+#
+# Detect target branch
+#
 BRANCH=""
 if test -n "$PUSHED_REF"; then
     if [[ "$PUSHED_REF" = refs/heads/* ]]; then
@@ -46,6 +49,10 @@ if test -n "$PUSHED_REF"; then
     fi
 fi
 
+# Switch orchestra to that branch too, if it exists
+git fetch
+git checkout "$BRANCH" || true
+
 #
 # Install orchestra
 #