Fix configuration for Packit 1.0.0

This commit fixes the configuration for the forthcoming Packit 1.0.0.
See [our blog post](https://packit.dev/posts/packit_1_0_0_action_required) for more details.
  - Job type `build` has been changed to `copr_build`.
  - Job type `production_build` has been changed to `upstream_koji_build`.
  - Key `upstream_project_name` has been changed to `upstream_package_name`.
  - Key `synced_files` has been changed to `files_to_sync`.

Please review and merge me before January 2025 otherwise packit-service jobs will fail because of an invalid configuration.

.packit.yaml

@@ -1,6 +1,6 @@
 specfile_path: libxcrypt.spec
 
-synced_files:
+files_to_sync:
   - libxcrypt.spec
   - .packit.yaml
 
@@ -15,14 +15,14 @@ actions:
   post-upstream-clone: "wget https://src.fedoraproject.org/rpms/libxcrypt/raw/main/f/libxcrypt.spec -O libxcrypt.spec"
 
 jobs:
-- job: production_build
+- job: upstream_koji_build
   trigger: commit
   metadata:
     branch: develop
     scratch: true
     targets: rawhide
 
-- job: production_build
+- job: upstream_koji_build
   trigger: pull_request
   metadata:
     scratch: true