fix(db): grant write access to project_memberships table

project_memberships is mutated at runtime but was missing from the
testgen_execute_role write-grant list, so membership changes failed with a
permission error. Applied on existing deployments via the grant refresh on
upgrade; no migration needed.

Author: aarthy-dk

testgen/template/dbsetup/075_grant_role_rights.sql

@@ -44,6 +44,7 @@ GRANT SELECT, INSERT, DELETE, UPDATE ON
     {SCHEMA_NAME}.job_executions,
     {SCHEMA_NAME}.settings,
     {SCHEMA_NAME}.notification_settings,
+    {SCHEMA_NAME}.project_memberships,
     {SCHEMA_NAME}.test_definition_notes,
     {SCHEMA_NAME}.oauth2_clients,
     {SCHEMA_NAME}.oauth2_authorization_codes,