Add Depedabot and tweak ModifierAst

.github/dependabot.yml

@@ -0,0 +1,12 @@
+version: 2
+updates:
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+
+  - package-ecosystem: "nuget"
+    directory: "/"
+    schedule:
+      interval: "weekly"

GqlPlus.sln

@@ -22,6 +22,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 		.prettierrc.yml = .prettierrc.yml
 		coverage.ps1 = coverage.ps1
 		coverage.runsettings = coverage.runsettings
+		.github\dependabot.yml = .github\dependabot.yml
 		Directory.Build.props = Directory.Build.props
 		.github\workflows\dotnet-test.yml = .github\workflows\dotnet-test.yml
 	EndProjectSection

src/GqlPlus.Verifier/Ast/ModifierAst.cs

@@ -47,5 +47,5 @@ internal enum ModifierKind
 
 public interface IAstModified
 {
-  ModifierAst[] Modifiers { get; set; }
+  ModifierAst[] Modifiers { get; }
 }