Fix decimal literal

Author: hadashiA

src/MemoryPack.Generator/MemoryPackGenerator.Emitter.cs

@@ -1376,7 +1376,7 @@ string EmitConstantValue(object? constantValue)
                 string x => $"\"{x}\"",
                 char x => $"'{x}'",
                 float x => $"{x}f",
-                decimal x => $"{x}D",
+                decimal x => $"{x}M",
                 bool x => x ? "true" : "false",
                 _ => constantValue.ToString()
             };

tests/MemoryPack.Tests/Models/DefaultValues.cs

@@ -46,7 +46,7 @@ partial class CtorParamDefaultValue
     public bool B;
 
     [MemoryPackConstructor]
-    public CtorParamDefaultValue(int x, int y = 12345, float z = 678.9f, string s = "aaaaaa", bool b = true)
+    public CtorParamDefaultValue(int x, int y = 12345, float z = 678.9f, string s = "aaaaaa", bool b = true, decimal d = 99M)
     {
         X = x;
         Y = y;