pylint fixes: arguments-differ
pylint fixes: arguments-differ

Rename argument `value` => `o` to match the argument name in
`json.JSONEncoder.default`.

Fixes:

[W0221(arguments-differ), _ArgsEncoder.default] Parameters differ from overridden 'default' method

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester