Add |to_json to some values

roles/matrix-synapse/templates/synapse/homeserver.yaml.j2

@@ -934,18 +934,18 @@ url_preview_accept_language:
 # This homeserver's ReCAPTCHA public key. Must be specified if
 # enable_registration_captcha is enabled.
 #
-recaptcha_public_key: {{ matrix_synapse_recaptcha_public_key }}
+recaptcha_public_key: {{ matrix_synapse_recaptcha_public_key|to_json }}
 
 # This homeserver's ReCAPTCHA private key. Must be specified if
 # enable_registration_captcha is enabled.
 #
-recaptcha_private_key: {{ matrix_synapse_recaptcha_private_key }}
+recaptcha_private_key: {{ matrix_synapse_recaptcha_private_key|to_json }}
 
 # Uncomment to enable ReCaptcha checks when registering, preventing signup
 # unless a captcha is answered. Requires a valid ReCaptcha
 # public/private key. Defaults to 'false'.
 #
-enable_registration_captcha: {{ matrix_synapse_enable_registration_captcha }}
+enable_registration_captcha: {{ matrix_synapse_enable_registration_captcha|to_json }}
 
 # The API endpoint to use for verifying m.login.recaptcha responses.
 # Defaults to "https://www.recaptcha.net/recaptcha/api/siteverify".