fix logging: make variable const-correct

Detected with clang-tidy:

```
<hidden by NDA>: error: variable 'module' of type '::logging::Module' can be declared 'const' [misc-const-correctness,-warnings-as-errors]
    LOG_DEBUG() << "<hidden by NDA>";
    ^
<hidden by NDA>/universal/include/userver/logging/log.hpp:270:52: note: expanded from macro 'LOG_DEBUG'
#define LOG_DEBUG() USERVER_IMPL_LOGS_DEBUG_ERASER(LOG(USERVER_NAMESPACE::logging::Level::kDebug))
                                                   ^
<hidden by NDA>/universal/include/userver/logging/log.hpp:260:18: note: expanded from macro 'LOG'
#define LOG(lvl) LOG_TO(USERVER_NAMESPACE::logging::GetDefaultLogger(), (lvl))
                 ^
<hidden by NDA>/universal/include/userver/logging/log.hpp:254:11: note: expanded from macro 'LOG_TO'
        : USERVER_IMPL_LOG_TO((logger), (lvl))
          ^
<hidden by NDA>/universal/include/userver/logging/log.hpp:225:13: note: expanded from macro 'USERVER_IMPL_LOG_TO'
            static USERVER_NAMESPACE::logging::Module module(location);         \
            ^
```

Tests: CI
commit_hash:76344878157d5c5388ec39739195ee2c7e0762dc

universal/include/userver/logging/log.hpp

@@ -222,7 +222,7 @@ struct EntryStorage final {
         logger,                                                                 \
         level,                                                                  \
         [](const auto& location) -> const USERVER_NAMESPACE::logging::Module& { \
-            static USERVER_NAMESPACE::logging::Module module(location);         \
+            static const USERVER_NAMESPACE::logging::Module module(location);   \
             return module;                                                      \
         }(USERVER_NAMESPACE::utils::impl::SourceLocation::Current()),           \
         USERVER_NAMESPACE::logging::LogClass::kLog                              \