Fix typo

Also to be consistent with dm_api.proto which is used on DMServer:
cl/293161272.

The field is not yet used anywhere, so it's safe to rename.

Change-Id: Ib348ae4c0504a71cfebf0df516b26afecfb971e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2035988Reviewed-by: Pavol Marko <pmarko@chromium.org>
Commit-Queue: Askar Aitzhan <askaraitzhan@google.com>
Cr-Commit-Position: refs/heads/master@{#738369}

components/policy/proto/device_management_backend.proto

@@ -3002,7 +3002,7 @@ message DeviceManagementRequest {
 
   // Request to start / continue client certificate provisioning process.
   optional ClientCertificateProvisioningRequest
-      client_certificate_provisionining_request = 34;
+      client_certificate_provisioning_request = 34;
 
   // Next id: 35.
 }