setup: bump formencode minimum version to 1.3.0 The formencode version range included both 1.2.x and 1.3.x releases. However, since 1.3.0, _to_python and validate_python are deprecated and renamed to _convert_to_python and _validate_python, respectively. With current pytest, these (long) deprecation warnings are shown in the test logs. There are two options: - restrict maximum version to 1.2.x - bump minimum version to 1.3.x In this commit we choose the latter approach, going towards the future rather than the past.