guix: Use DOS newlines for SHA256SUMS files

OpenPGP specifies that plain text should use CR LF for newlines.
By doing so, it becomes possible to include the hashes directly in the .asc file.

contrib/guix/guix-attest

@@ -174,6 +174,10 @@ basenameify_SHA256SUMS() {
     sed -E 's@(^[[:xdigit:]]{64}[[:space:]]+).+/([^/]+$)@\1\2@'
 }
 
+unix2dos() {
+    sed 's/$/\r/'
+}
+
 outsigdir="$GUIX_SIGS_REPO/$VERSION/$signer_name"
 mkdir -p "$outsigdir"
 (
@@ -187,6 +191,7 @@ mkdir -p "$outsigdir"
             | sort -u \
             | sort -k2 \
             | basenameify_SHA256SUMS \
+            | unix2dos \
                 > "$temp_noncodesigned"
         if [ -e noncodesigned.SHA256SUMS ]; then
             # The SHA256SUMS already exists, make sure it's exactly what we
@@ -215,6 +220,7 @@ mkdir -p "$outsigdir"
             | sort -u \
             | sort -k2 \
             | basenameify_SHA256SUMS \
+            | unix2dos \
                 > "$temp_all"
         if [ -e all.SHA256SUMS ]; then
             # The SHA256SUMS already exists, make sure it's exactly what we