refactor(GitVersion.Configuration): do not assign value to AssemblyInformationalFormat

The tests expect this to be null

Author: BinToss

src/GitVersion.Configuration/GitVersionConfiguration.cs

@@ -35,7 +35,7 @@ internal sealed record GitVersionConfiguration : BranchConfiguration, IGitVersio
     [JsonPropertyName("assembly-informational-format")]
     [JsonPropertyDescription($"Specifies the format of AssemblyInformationalVersion. Defaults to '{DefaultAssemblyInformationalFormat}'.")]
     [JsonPropertyDefault(DefaultAssemblyInformationalFormat)]
-    public string? AssemblyInformationalFormat { get; internal set; } = DefaultAssemblyInformationalFormat;
+    public string? AssemblyInformationalFormat { get; internal set; }
 
     [JsonPropertyName("assembly-versioning-format")]
     [JsonPropertyDescription("Specifies the format of AssemblyVersion and overwrites the value of assembly-versioning-scheme.")]