Collect failed keys and print them at the end

Since !180, all keys are tried. This can indeed be useful but buries
the offending key in a long output log.

This stores a message containing the key and UID during processing and
prints them all at the end.

wkd_sync/archlinux-keyring-wkd-sync

@@ -42,7 +42,6 @@ gpg_locate_external=(
 fingerprint_mboxes="$(
     gpg --homedir "$homedir" --no-permission-warning --list-keys --list-options show-only-fpr-mbox
 )"
-error=0
 
 # a list of <fingerprints> of all revoked keys and keys that have no valid main
 # key signatures
@@ -56,16 +55,20 @@ if (( EUID != 0 )); then
      exit 1
 fi
 
+errors=()
 # first update the main signing keys, then the packager keys
 for domain_match in "$main_key_domain_match" "$packager_domain_match"; do
     while read -ra fpr_email; do
         if [[ ${fpr_email[1]} =~ $domain_match && ! "$old_fingerprints" =~ ${fpr_email[0]} && ! "${invalid_fingerprints[*]}" =~ ${fpr_email[0]} ]]; then
             printf "Refreshing key %s with UID %s...\n" "${fpr_email[0]}" "${fpr_email[1]}"
-            "${gpg_locate_external[@]}" "${fpr_email[1]}" || let ++error
+            if ! "${gpg_locate_external[@]}" "${fpr_email[1]}"; then
+                errors+=("Error refreshing key ${fpr_email[0]} with UID ${fpr_email[1]}.")
+            fi
         else
             printf "Skipping key %s with UID %s...\n" "${fpr_email[0]}" "${fpr_email[1]}"
         fi
     done <<< "$fingerprint_mboxes"
 done
 
-exit ${error}
+>&2 printf "%s\n" "${errors[@]}"
+exit ${#errors[@]}