Mostly, the code used to allow having either --author or --name,
while it should use either both (when generating metadata) or
neither (when using a metadata file).

This code fixes this, and also catches some more invalid cases.

This uses a context-manager instead of manually handling
removing the file.

'return' statements were ignored, and log level was too low for an error.

Related to 0a9ec2a9

The deposit service only sends message for the current new deposit loader.

Related to T2140

Current djangos-stubs version (1.2.0) is not compatible with latest mypy one (0.750).
So pin their version until the issue is fixed.

Related T2024

so pre-commit is happy.

hat tip to @anlambert for the tip

make mypy 0.730 pass cleanly again

This reverts commit 12e3966b.