test: fix sources unit test to call SRC_ReportSource() correctly

Call the function with current time instead of latest sample of the
first source to avoid undefined conversion of negative double to long
int.

Fixes: 07600cbd71 ("test: extend sources unit test")

test/unit/sources.c

@@ -190,6 +190,7 @@ test_unit(void)
     }
 
     for (j = 0; j < sizeof (srcs) / sizeof (srcs[0]); j++) {
+      SCH_GetLastEventTime(&sample.time, NULL, NULL);
       SRC_ReportSource(j, &report, &sample.time);
       SRC_DestroyInstance(srcs[j]);
     }