fix: Attempt 2 for unbound variable fix

Containerfile

@@ -43,6 +43,9 @@ ARG SOURCE_TAG="latest"
 ## this is a standard Containerfile FROM using the build ARGs above to select the right upstream image
 FROM ghcr.io/ublue-os/${SOURCE_IMAGE}${SOURCE_SUFFIX}:${SOURCE_TAG}
 
+ARG SOURCE_IMAGE="${SOURCE_IMAGE}"
+ARG SOURCE_SUFFIX="${SOURCE_SUFFIX}"
+ARG SOURCE_TAG="${SOURCE_TAG}"
 
 ### 3. MODIFICATIONS
 ## make modifications desired in your image and install packages by modifying the build.sh script