chore: update golangci-lint to v2.13.0

Migrate the deprecated gofumpt `extra-rules` to `extra.group-params`, as
the alias now also enables the new `clothe-returns` and `balance-calls`
rules. Disable SA4023, which hangs on go 1.27, see
https://github.com/golangci/golangci-lint/issues/6732.

Apply the resulting modernize fixes, mostly flattening embedded struct
literals and switching errors.As to errors.AsType.

Assisted-by: Claude:Opus 5

services/auth/source/oauth2/source_sync_test.go

@@ -18,14 +18,12 @@ func TestSource(t *testing.T) {
 
 	source := &Source{
 		Provider: "fake",
-		ConfigBase: auth.ConfigBase{
-			AuthSource: &auth.Source{
-				ID:            12,
-				Type:          auth.OAuth2,
-				Name:          "fake",
-				IsActive:      true,
-				IsSyncEnabled: true,
-			},
+		AuthSource: &auth.Source{
+			ID:            12,
+			Type:          auth.OAuth2,
+			Name:          "fake",
+			IsActive:      true,
+			IsSyncEnabled: true,
 		},
 	}