Only create release on tag or promotion

Signed-off-by: Jacob Kiers <jacob@jacobkiers.net>

.drone.jsonnet

@@ -81,6 +81,9 @@ local add_build_steps() = [
           files: 'artifacts/*',
           checksum: 'sha256',
         },
+        when: {
+          event: ['tag', 'promote'],
+        },
       },
     ],