Fix Vultr startup script JSON serialization error

The startup_script module was failing with "Object of type 'bytes' is not
JSON serializable" because the lookup('template', ...) was returning bytes
instead of a string.

Added | string filter to explicitly convert the template result to a
string, matching the pattern used by the DigitalOcean cloud provider.

Also simplified from multiline block format to inline format for
consistency with other cloud providers.

Fixes the error: "Object of type 'bytes' is not JSON serializable by the
'tagless' profile."

Author: fank

roles/cloud-vultr/tasks/main.yml

@@ -28,8 +28,7 @@
     - name: Upload the startup script
       vultr.cloud.startup_script:
         name: algo-startup
-        script: |
-          {{ lookup('template', 'files/cloud-init/base.yml') }}
+        script: "{{ lookup('template', 'files/cloud-init/base.yml') | string }}"
 
     - name: Creating a server
       vultr.cloud.instance: