improve: use context.Background instead of context.TODO

[sivchari]

Description

I changed context.TODO to context.Background. context.Background equals context.TODO, so this change doesn't affect to any libs. But it's clear that the current implementation uses context, so we should use context.Background instead of context.TODO.

Checklist

• [x] Code compiles correctly
• [x] Run make fmt to fix inconsistent formats
• [x] Run make lint to get lint errors and fix all of them
• [x] Created tests which fail without the change (if possible)
• [x] All tests passing
• [x] Extended the README / documentation, if necessary