chore(deps): update ghcr.io/element-hq/synapse docker tag to v1.121.1

roles/custom/matrix-synapse/defaults/main.yml

@@ -16,7 +16,7 @@ matrix_synapse_enabled: true
 matrix_synapse_github_org_and_repo: element-hq/synapse
 
 # renovate: datasource=docker depName=ghcr.io/element-hq/synapse
-matrix_synapse_version: v1.120.2
+matrix_synapse_version: v1.121.1
 
 matrix_synapse_username: ''
 matrix_synapse_uid: ''