fix(tem): fix spf record example (scaleway#3829)

Author: bene2k1

managed-services/transactional-email/how-to/add-spf-dkim-records-to-your-domain.mdx

@@ -28,8 +28,8 @@ After you have configured your domain with Transactional Email, you are prompted
 2. Click your domain. You are redirected to the SPF, DKIM and MX configuration page.
 3. Copy the value that applies to your case to add an SPF record.
     <Message type="important">
-     - If you have no SPF record on this domain, copy the following value: `v=spf1 include:_spf.tem.scaleway.com/ -all`
-     - If you already have configured an SPF record, copy the following value: `include:_spf.tem.scaleway.com/`
+     - If you have no SPF record on this domain, copy the following value: `v=spf1 include:_spf.tem.scaleway.com -all`
+     - If you already have configured an SPF record, copy the following value: `include:_spf.tem.scaleway.com`
     </Message>
 
 4. Add a `TXT` record type in the root zone of your domain on your DNS zone.