Fix Shellcheck SC1091: Can't follow file

Not following: (error message here)

https://github.com/koalaman/shellcheck/wiki/SC1091

Signed-off-by: Dan Callahan <danc@element.io>

debian/matrix-synapse-py3.config

@@ -2,6 +2,7 @@
 
 set -e
 
+# shellcheck disable=SC1091
 . /usr/share/debconf/confmodule
 
 # try to update the debconf db according to whatever is in the config files

debian/matrix-synapse-py3.postinst

@@ -1,5 +1,6 @@
 #!/bin/sh -e
 
+# shellcheck disable=SC1091
 . /usr/share/debconf/confmodule
 
 CONFIGFILE_SERVERNAME="/etc/matrix-synapse/conf.d/server_name.yaml"