Content of ComplexInput with a custom format is not copied to a temporary file.

[sum1lim]

Describe the bug
A ComplexInput with a custom format Format(mime_type="text/x-yaml", extension=".yaml",) is used in wps_update_metadata, but the content of the input is not being copied to a temporary file or a temporary file is not even created. Normally, a file named tmp/[pywps_temporary_dir]/input.[extension_defined] is created when using a pre-defined ComplexInput.

To Reproduce

1. Do the followings when running wps_update_metadata with local updates yaml file input.
2. Print out the output of vars(request.inputs["updates_file"][0]) and check the _file attribute.
3. If the file is created, check the content in it by reading the file.
4. Try the procedure in various environments.

Expected behavior
The content of the ComplexInput with a custom format is copied to tmp/[pywps_temporary_dir]/input.[extension_defined].