fix: Default deserialize for compatibility_mode

changelog.d/+6d0bc844.bugfix.md

@@ -0,0 +1 @@
+Fixed `global.oauth.compatibility_mode` being required, despite being ignored, when the `[global.oauth.oidc]` config section is provided.

src/core/config/mod.rs

@@ -2442,6 +2442,7 @@ pub struct OauthConfig {
 	///   legacy authentication will be unable to log in.
 	///
 	/// default: "hybrid"
+	#[serde(default)]
 	compatibility_mode: OAuthMode,
 
 	/// display: hidden