Remove useless go.sum and CI check

[silvanocerza]

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• Tests for the changes have been added (for bug fixes / features)
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What kind of change does this PR introduce?

CI enhancement.

What is the current behavior?

go mod tidy is run in CI two times for the root project since term_example only has a go.sum but no go.mod file.

What is the new behavior?

go mod tidy is now run only once for the root project since no check is necessary for term_example as it doesn't have a go.mod file. go.sum for term_example has been removed too.

Does this PR introduce a breaking change, and is titled accordingly?

Nope.

Other information

Change stems from this comment.