Make detection for test-binary more universal

[thaJeztah]

• relates to https://github.com/spf13/cobra/pull/155
• relates to https://github.com/docker/cli/pull/5224

When running tests in verbose mode (or other options), tests involving Cobra may fail if the test does not explicitly set Command.args to an empty slice; in this case, Cobra defaults to using os.Args, which will contain arguments passed to the test (such as -v (verbose)).

Commits e5762054c9a6429fa7c234897707d and 1ef0913976db2004980575ed815c3 implemented a workaround for this when running (unit) tests for Cobra itself, but this check is specifig to Cobra (checking for cobra.test), and don't work on Windows (which will have a .exe extension),

This patch implements a more universal check, so that users of Cobra as a module also benefit from this workaround.

go1.21 and up provides a testing.Testing() utility (1); as the Cobra module still supports Go1.16 and up, an alternative implementation was added for older versions, based on golang.org/x/mod/lazyregexp 2.