Manager: store the jobs implicit variable in platform-native notation

Don't change backslashes to forward slashes on Windows. Trying to use
forward slashes everywhere was a mistake, and this is one of the steps to
make it right.

internal/manager/config/config.go

@@ -291,7 +291,7 @@ func (c *Conf) addImplicitVariables() {
 			{
 				Audience: VariableAudienceAll,
 				Platform: VariablePlatformAll,
-				Value:    crosspath.ToSlash(c.EffectiveStoragePath()),
+				Value:    c.EffectiveStoragePath(),
 			},
 		},
 	}