Remove deprecated `ioutil.ReadAll`

[pedromotita]

Description

Replace ioutil.ReadAll with io.ReadAll.

Some tests in command_test.go use the ioutil.ReadAll function from io/ioutils package. This package is deprecated as of Go 1.16, and the documentation advises to replace it with io.ReadAll

References

• io/ioutil package documentation: https://pkg.go.dev/io/ioutil
• ioutil.ReadAll documentation: https://pkg.go.dev/io/ioutil#ReadAll