gpib: do not import GpibError from Gpib since it lives in gpib module

[MatthieuDartiailh]

• [x] Closes #245 (insert issue number if relevant)
• [x] Executed black . && isort -c . && flake8 with no errors
• [x] Added an entry to the CHANGES file

@charkster can you confirm it fixes your issue ?

[MatthieuDartiailh]

bors try

[bors[bot]]

try

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[MatthieuDartiailh]

Merging since this should work and I need the cis fix in.

@charkster please confirm this addressed your issue when you can.

bors r+

[bors[bot]]

Build succeeded:

• Check code formatting
• Docs building
• Tests result