test: env: Enable env unit tests by default

If CONFIG_UNIT_TEST is enabled we should enable the individual tests by
default to ensure good test coverage.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/test/env/Kconfig b/test/env/Kconfig
index ff16413..6cb8233 100644
--- a/test/env/Kconfig
+++ b/test/env/Kconfig
@@ -1,6 +1,7 @@
 config UT_ENV
 	bool "Enable env unit tests"
 	depends on UNIT_TEST
+	default y
 	help
 	  This enables the 'ut env' command which runs a series of unit
 	  tests on the env code.