[debian] fix grep_dd_sigs & shellcheck

Without quoting "$sigs", this was making the script output nothing:
    echo $sigs | while read

debian/grep_dd_sigs

@@ -24,13 +24,13 @@ if [ $# -ne 1 ] ; then
 	exit 1
 fi
 
-sigs=$(gpg --with-colons --check-sigs $1 \
+sigs=$(gpg --with-colons --check-sigs "$1" \
 	| grep "sig:\!" \
 	| sed -r "s/sig:\!::[[:digit:]]+:([[:alnum:]]+):.*$/\1/")
 
-echo $sigs | while read key
+echo "$sigs" | while read -r key
 	do
-		gpg --no-default-keyring --keyring /usr/share/keyrings/debian-keyring.gpg --list-keys $key 2>/dev/null \
+		gpg --no-default-keyring --keyring /usr/share/keyrings/debian-keyring.gpg --list-keys "$key" 2>/dev/null \
 			| grep "debian.org" \
 			| grep "^uid" \
 			| sed -r "s/^uid +//" \