simple: detect errors created just for logging

[ainar-g]

Another from an old project of mine. Code like this:

log.Print(errors.New("oh no"))

log.Print(fmt.Errorf("oh no: %w", err))

Should really be this:

log.Print("oh no")

log.Printf("oh no: %s", err)

Same with testing helpers.

[ainar-g]

This is very similar to #143.

[dominikh]

Weirdest offender I've found today: panic(fmt.Errorf("...")) (yes, there were no format specifiers in the string.)

[ainar-g]

That one might actualy sort of make sense if there is a panic handler upstack that distinguishes between error and non-error recover return-values. Although in this particular case one would probably just use errors.New.