CI(appveyor): Use release signing

Apparently we have been using our test certificate for signing our
released binaries so far.
This is obviously not what we want, so this commit changes this so now
the actual (proper) certificate will be used.

(cherry picked from commit ab04c58)

Author: Krzmbrzl

.appveyor.yml

@@ -43,6 +43,6 @@ artifacts:
 
 deploy:
   - provider: Webhook
-    url: https://app.signpath.io/API/v1/79916aba-7a9f-448d-91c6-fb83593b59d3/Integrations/AppVeyor?ProjectSlug=mumble&SigningPolicySlug=test-signing
+    url: https://app.signpath.io/API/v1/79916aba-7a9f-448d-91c6-fb83593b59d3/Integrations/AppVeyor?ProjectSlug=mumble&SigningPolicySlug=release-signing
     authorization:
       secure: WKbGSfFSHTtODf6eHRSHPAobctJli48O/VoMpCYTuIlITl2piOpCH6igCRDX4EuJTzgDX45H34tVfPuNzSMdLA==