dns_dynu: use mutable conf storage so newly exported credentials win

Same stale-account.conf override as dns_dnsimple: the sourced plain
copy shadowed newly exported Dynu_ClientId/Dynu_Secret.

https://github.com/acmesh-official/acme.sh/issues/3216

dnsapi/dns_dynu.sh

@@ -23,6 +23,8 @@ dns_dynu_add() {
   fulldomain=$1
   txtvalue=$2
 
+  Dynu_ClientId="${Dynu_ClientId:-$(_readaccountconf_mutable Dynu_ClientId)}"
+  Dynu_Secret="${Dynu_Secret:-$(_readaccountconf_mutable Dynu_Secret)}"
   if [ -z "$Dynu_ClientId" ] || [ -z "$Dynu_Secret" ]; then
     Dynu_ClientId=""
     Dynu_Secret=""
@@ -32,8 +34,8 @@ dns_dynu_add() {
   fi
 
   #save the client id and secret to the account conf file.
-  _saveaccountconf Dynu_ClientId "$Dynu_ClientId"
+  _saveaccountconf_mutable Dynu_ClientId "$Dynu_ClientId"
-  _saveaccountconf Dynu_Secret "$Dynu_Secret"
+  _saveaccountconf_mutable Dynu_Secret "$Dynu_Secret"
 
   if [ -z "$Dynu_Token" ]; then
     _info "Getting Dynu token."
@@ -69,6 +71,8 @@ dns_dynu_rm() {
   fulldomain=$1
   txtvalue=$2
 
+  Dynu_ClientId="${Dynu_ClientId:-$(_readaccountconf_mutable Dynu_ClientId)}"
+  Dynu_Secret="${Dynu_Secret:-$(_readaccountconf_mutable Dynu_Secret)}"
   if [ -z "$Dynu_ClientId" ] || [ -z "$Dynu_Secret" ]; then
     Dynu_ClientId=""
     Dynu_Secret=""
@@ -78,8 +82,8 @@ dns_dynu_rm() {
   fi
 
   #save the client id and secret to the account conf file.
-  _saveaccountconf Dynu_ClientId "$Dynu_ClientId"
+  _saveaccountconf_mutable Dynu_ClientId "$Dynu_ClientId"
-  _saveaccountconf Dynu_Secret "$Dynu_Secret"
+  _saveaccountconf_mutable Dynu_Secret "$Dynu_Secret"
 
   if [ -z "$Dynu_Token" ]; then
     _info "Getting Dynu token."