Update .NET MGCB tools to 3.8.4

Author: renovate[bot]

test/MonoGameSolution/.config/dotnet-tools.json

@@ -3,13 +3,13 @@
   "isRoot": true,
   "tools": {
     "dotnet-mgcb-editor-mac": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb-editor-mac"
       ]
     },
     "dotnet-mgcb-editor": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb-editor"
       ]

test/MonoGameSolution/Desktop381/.config/dotnet-tools.json

@@ -3,31 +3,31 @@
   "isRoot": true,
   "tools": {
     "dotnet-mgcb": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb"
       ]
     },
     "dotnet-mgcb-editor": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb-editor"
       ]
     },
     "dotnet-mgcb-editor-linux": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb-editor-linux"
       ]
     },
     "dotnet-mgcb-editor-windows": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb-editor-windows"
       ]
     },
     "dotnet-mgcb-editor-mac": {
-      "version": "3.8.1.303",
+      "version": "3.8.4",
       "commands": [
         "mgcb-editor-mac"
       ]