guix: Zip needs to include all files with time as SOURCE_DATE_EPOCH

The zip for codesigned MacOS distribution needs to have all files have
the same timestamp. These files also need to be included in the zip as
zip is not automatically recursive. We use the same pattern for zip as
is done for the other zip files produced by guix.

contrib/guix/libexec/codesign.sh

@@ -86,7 +86,11 @@ mkdir -p "$DISTSRC"
             signapple apply dist/Bitcoin-Qt.app codesignatures/osx/dist
 
             # Make a .zip from dist/
-            zip "${OUTDIR}/${DISTNAME}-${HOST}.zip" dist/*
+            cd dist/
+            find . -print0 \
+                | xargs -0r touch --no-dereference --date="@${SOURCE_DATE_EPOCH}"
+            find . | sort \
+                | zip -X@ "${OUTDIR}/${DISTNAME}-${HOST}.zip"
             ;;
         *)
             exit 1