Manager: always set config.currentGOOS

This variable is used in tests to mock the current OS, but wasn't set
during normal operation of the Manager. This caused issues with the
two-way variable system.

internal/manager/config/config.go

@@ -174,6 +174,7 @@ func DefaultConfig(override ...func(c *Conf)) Conf {
 		panic(fmt.Sprintf("unable to create copy of default config: %v", err))
 	}
 	c.Meta.Version = latestConfigVersion
+	c.currentGOOS = VariablePlatform(runtime.GOOS)
 	c.processAfterLoading(override...)
 	return *c
 }