sibon: Add product_manifest.xml to exclusion list

product_manifest.xml does not necessarily get built for all targets
but it has been added in AOSP build system.

Add this to the exclusion list while checking for existance of
all PRODUCT_PACKAGES components.

Issue: FP3-A11#404
Change-Id: I5a62c34f9a0a546b1d8d512e69b0afd40d15801b
diff --git a/fp3_sibon.mk b/fp3_sibon.mk
index c551787..e07386a 100644
--- a/fp3_sibon.mk
+++ b/fp3_sibon.mk
@@ -15,7 +15,7 @@
 
 $(call inherit-product, device/fairphone/fp3-sibon/device.mk)
 
-$(call enforce-product-packages-exist,)
+$(call enforce-product-packages-exist,product_manifest.xml)
 
 PRODUCT_NAME := fp3_sibon
 PRODUCT_FLAVOR := sibon