fix: Make plugin test resolve latest version

[maciektr]

Summary

If --asdf-tool-version=latest is passed to plugin test, it should resolve the version correctly, instead of passing latest directly.
This change mimics the one of the old bash plugin:

asdf/lib/commands/command-plugin-test.bash

Lines 129 to 138 in 31e8c93

	# Use the version passed in if it was set. Otherwise grab the latest
	# version from the versions list
	if [ -z "$tool_version" ] || [[ "$tool_version" == *"latest"* ]]; then
	version="$(latest_command "$plugin_name" "$(sed -e 's#latest##;s#^:##' <<<"$tool_version")")"
	if [ -z "$version" ]; then
	fail_test "could not get latest version"
	fi
	else
	version="$tool_version"
	fi

It also adds a test case to ensure correct behaviour of the changed code.

Fixes: #2193

Other Information