Add SLES and Leap 15.6

There are three changes here:

* openSUSE Leap 15.6 got released and will be maintained at least until
  end of Dec 2025.
* SLES 15.6 is going to be announced shortly and hence the overlapping
  lifecycle for 15.5 shortens its lifecycle to the end of calendar year
  2024.
* SLES 15 got a lifecycle extension. General support got 3 more years
  post-initial release added, hence end of life moves from 2028 to 2031.

pkg/detector/ospkg/suse/suse.go

@@ -39,9 +39,10 @@ var (
 		"15.2": time.Date(2021, 12, 31, 23, 59, 59, 0, time.UTC),
 		"15.3": time.Date(2022, 12, 31, 23, 59, 59, 0, time.UTC),
 		"15.4": time.Date(2023, 12, 31, 23, 59, 59, 0, time.UTC),
-		"15.5": time.Date(2028, 12, 31, 23, 59, 59, 0, time.UTC),
+		"15.5": time.Date(2024, 12, 31, 23, 59, 59, 0, time.UTC),
+		"15.6": time.Date(2031, 7, 31, 23, 59, 59, 0, time.UTC),
 		// 6 months after SLES 15 SP7 release
-		// "15.6": time.Date(2028, 12, 31, 23, 59, 59, 0, time.UTC),
+		// "15.7": time.Date(2031, 7, 31, 23, 59, 59, 0, time.UTC),
 	}
 
 	opensuseEolDates = map[string]time.Time{
@@ -55,6 +56,7 @@ var (
 		"15.3": time.Date(2022, 11, 30, 23, 59, 59, 0, time.UTC),
 		"15.4": time.Date(2023, 11, 30, 23, 59, 59, 0, time.UTC),
 		"15.5": time.Date(2024, 12, 31, 23, 59, 59, 0, time.UTC),
+		"15.6": time.Date(2025, 12, 31, 23, 59, 59, 0, time.UTC),
 	}
 )