Revert "chore(deps): update ghcr.io/element-hq/synapse docker tag to v1.142.0"

This reverts commit c8c6a83ecc.

Synapse v1.142.0 is broken for Matrix Authentication Service deployments
that use a path-prefix (e.g. `/auth`) such as ours.

For such deployments, Synapse fails to contact MAS at the correct
introspection endpoint (it keeps hitting `/oauth2/introspect`, instead of `/auth/oauth2/introspect`)
and is not usable.

Related to 3595ff921f

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: v1.142.0
+matrix_synapse_version: v1.141.0
 
 matrix_synapse_username: ''
 matrix_synapse_uid: ''