Add missing migration

sqitch/deploy/system_test_tables.sql

@@ -0,0 +1,21 @@
+-- Deploy guix-data-service:system_test_tables to pg
+
+BEGIN;
+
+CREATE TABLE system_tests (
+  id integer NOT NULL GENERATED ALWAYS AS IDENTITY,
+  name varchar NOT NULL,
+  description varchar NOT NULL,
+  location_id integer NOT NULL REFERENCES locations (id),
+  PRIMARY KEY (name, description, location_id),
+  UNIQUE (id)
+);
+
+CREATE TABLE guix_revision_system_test_derivations (
+  guix_revision_id integer NOT NULL REFERENCES guix_revisions (id),
+  system_test_id integer NOT NULL REFERENCES system_tests (id),
+  derivation_id integer NOT NULL REFERENCES derivations (id),
+  PRIMARY KEY (guix_revision_id, system_test_id, derivation_id)
+);
+
+COMMIT;

sqitch/revert/system_test_tables.sql

@@ -0,0 +1,8 @@
+-- Revert guix-data-service:system_test_tables from pg
+
+BEGIN;
+
+DROP TABLE guix_revision_system_test_derivations;
+DROP TABLE system_tests;
+
+COMMIT;

sqitch/verify/system_test_tables.sql

@@ -0,0 +1,7 @@
+-- Verify guix-data-service:system_test_tables on pg
+
+BEGIN;
+
+-- XXX Add verifications here.
+
+ROLLBACK;