Revert accidental binary breaking change

Author: bkoelman

src/JsonApiDotNetCore/Queries/Parsing/QueryTokenizer.cs

@@ -1,3 +1,4 @@
+using System.Collections.ObjectModel;
 using System.Text;
 using JetBrains.Annotations;
 
@@ -6,17 +7,18 @@ namespace JsonApiDotNetCore.Queries.Parsing;
 [PublicAPI]
 public sealed class QueryTokenizer
 {
-    public static readonly Dictionary<char, TokenKind> SingleCharacterToTokenKinds = new()
-    {
-        ['('] = TokenKind.OpenParen,
-        [')'] = TokenKind.CloseParen,
-        ['['] = TokenKind.OpenBracket,
-        [']'] = TokenKind.CloseBracket,
-        ['.'] = TokenKind.Period,
-        [','] = TokenKind.Comma,
-        [':'] = TokenKind.Colon,
-        ['-'] = TokenKind.Minus
-    };
+    public static readonly IReadOnlyDictionary<char, TokenKind> SingleCharacterToTokenKinds = new ReadOnlyDictionary<char, TokenKind>(
+        new Dictionary<char, TokenKind>
+        {
+            ['('] = TokenKind.OpenParen,
+            [')'] = TokenKind.CloseParen,
+            ['['] = TokenKind.OpenBracket,
+            [']'] = TokenKind.CloseBracket,
+            ['.'] = TokenKind.Period,
+            [','] = TokenKind.Comma,
+            [':'] = TokenKind.Colon,
+            ['-'] = TokenKind.Minus
+        });
 
     private readonly string _source;
     private readonly StringBuilder _textBuffer = new();