Cleanup and bump required runtimes (#5139)

* Cleanup and bump required runtimes

* Put netcoreapp2.1 back, we run old vstest.console (like 16.11) on that in compatibility tests

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Co-authored-by: Jakub Jareš <me@jakubjares.com>

Author: Evangelink

global.json

@@ -11,17 +11,17 @@
         "2.1.30",
         "3.1.32",
         "5.0.17",
-        "6.0.29",
-        "7.0.18",
-        "8.0.4"
+        "6.0.32",
+        "7.0.20",
+        "8.0.7"
       ],
       "dotnet/x86": [
         "2.1.30",
         "3.1.32",
         "5.0.17",
-        "6.0.29",
-        "7.0.18",
-        "8.0.4"
+        "6.0.32",
+        "7.0.20",
+        "8.0.7"
       ]
     },
     "vs": {