Update to .NET Core SDK 3.1.302 (#681)

This change updates the .NET Core SDK used by the Actions Runner to
version 3.1.302 to address the issues that are caused by the following issue:
    https://github.com/dotnet/runtime/issues/13475
See #574 for more information.

Fixes #574

src/dev.sh

@@ -17,7 +17,7 @@ LAYOUT_DIR="$SCRIPT_DIR/../_layout"
 DOWNLOAD_DIR="$SCRIPT_DIR/../_downloads/netcore2x"
 PACKAGE_DIR="$SCRIPT_DIR/../_package"
 DOTNETSDK_ROOT="$SCRIPT_DIR/../_dotnetsdk"
-DOTNETSDK_VERSION="3.1.100"
+DOTNETSDK_VERSION="3.1.302"
 DOTNETSDK_INSTALLDIR="$DOTNETSDK_ROOT/$DOTNETSDK_VERSION"
 RUNNER_VERSION=$(cat runnerversion)
 

src/global.json

@@ -1,5 +1,5 @@
 {
   "sdk": {
-    "version": "3.1.100"
+    "version": "3.1.302"
   }
-}
+}