drm_hwcomposer: CI: Bump-up clang toolchain to v15

Address new clang-tidy findings, in most cases 'misc-const-correctness'
check was addressed by adding 'const' modifier, or in some cases changed
to 'auto' (where it's better for formatting).

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/backend/BackendManager.cpp b/backend/BackendManager.cpp
index 9bf6324..c1bc0f6 100644
--- a/backend/BackendManager.cpp
+++ b/backend/BackendManager.cpp
@@ -42,7 +42,7 @@
 }
 
 int BackendManager::SetBackendForDisplay(HwcDisplay *display) {
-  std::string driver_name(display->GetPipe().device->GetName());
+  auto driver_name(display->GetPipe().device->GetName());
   char backend_override[PROPERTY_VALUE_MAX];
   property_get("vendor.hwc.backend_override", backend_override,
                driver_name.c_str());