fix(matrix): Fix variable name

apps/base/matrix/synatainer.yaml

@@ -22,7 +22,7 @@ spec:
               seccompProfile:
                 type: RuntimeDefault
             env:
-              - name: PG_host
+              - name: DB_HOST
                 value: matrix-postgres.matrix.svc.cluster.local
               - name: DB_NAME
                 value: synapse