Add diagnostics_config to test databases in djls-semantic

Two test databases in djls-semantic also implement the Db trait and
need the diagnostics_config method:
- TestDatabase in blocks/tree.rs
- TestDatabase in semantic/forest.rs

Both return default config since tests don't need custom settings.

Author: claude

crates/djls-semantic/src/blocks/tree.rs

@@ -247,6 +247,10 @@ mod tests {
         fn template_dirs(&self) -> Option<Vec<Utf8PathBuf>> {
             None
         }
+
+        fn diagnostics_config(&self) -> djls_conf::DiagnosticsConfig {
+            djls_conf::DiagnosticsConfig::default()
+        }
     }
 
     #[test]

crates/djls-semantic/src/semantic/forest.rs

@@ -287,6 +287,10 @@ mod tests {
         fn template_dirs(&self) -> Option<Vec<Utf8PathBuf>> {
             None
         }
+
+        fn diagnostics_config(&self) -> djls_conf::DiagnosticsConfig {
+            djls_conf::DiagnosticsConfig::default()
+        }
     }
 
     #[test]