Move default case to statement outside switch block in log_severity.h.

Some compilers warn if a switch block that already covers all
enumeration values also has a default label.

PiperOrigin-RevId: 597583941
Change-Id: Ib3eb08dca0a19105522c61e47944cfc75280c15e

absl/base/log_severity.h

@@ -104,8 +104,8 @@ constexpr const char* LogSeverityName(absl::LogSeverity s) {
     case absl::LogSeverity::kWarning: return "WARNING";
     case absl::LogSeverity::kError: return "ERROR";
     case absl::LogSeverity::kFatal: return "FATAL";
-    default: return "UNKNOWN";
   }
+  return "UNKNOWN";
 }
 
 // NormalizeLogSeverity()