利用Directory.Build.props文件指定Unity使用C#9版本

Unity/Directory.Build.props

@@ -0,0 +1,5 @@
+<Project>
+  <PropertyGroup>
+    <LangVersion>9.0</LangVersion>
+  </PropertyGroup>
+</Project>

Unity/ProjectSettings/ProjectVersion.txt

@@ -1,2 +1,2 @@
-m_EditorVersion: 2020.3.26f1c1
-m_EditorVersionWithRevision: 2020.3.26f1c1 (cf0e0a163043)
+m_EditorVersion: 2021.3.3f1c1
+m_EditorVersionWithRevision: 2021.3.3f1c1 (d43514f36ab8)