Make go vet happy

[oerlikon]

It appears go vet isn't particularly happy about some example names in tests:

progressbar$ go vet .
# github.com/schollz/progressbar/v3
./progressbar_test.go:125:1: ExampleOptionShowCountBigNumber refers to unknown identifier: OptionShowCountBigNumber
./progressbar_test.go:146:1: ExampleOptionShowDescriptionAtLineEnd_WithSpinner refers to unknown field or method: OptionShowDescriptionAtLineEnd.WithSpinner
./progressbar_test.go:163:1: ExampleOptionChangeMax refers to unknown identifier: OptionChangeMax
./progressbar_test.go:171:1: ExampleIgnoreLength_WithIteration refers to unknown identifier: IgnoreLength
./progressbar_test.go:233:1: ExampleIgnoreLength_WithSpeed refers to unknown identifier: IgnoreLength

This change fixes it and adds go vet to the CI workflow.

[schollz]

Thanks, this looks great!!