Merge #21286: build: Bump minimum Qt version to 5.9.5

faa06ecc9c build: Bump minimum Qt version to 5.9.5 (Hennadii Stepanov)

Pull request description:

  Close #20104.

ACKs for top commit:
  laanwj:
    Code review ACK faa06ecc9c
  jarolrod:
    ACK faa06ecc9c
  fanquake:
    ACK faa06ecc9c - this should be ok to do now.

Tree-SHA512: 7295472b5fd37ffb30f044e88c39d375a5a5187d3f2d44d4e73d0eb0c7fd923cf9949c2ddab6cddd8c5da7e375fff38112b6ea9779da4fecce6f024d05ba9c08

src/qt/bitcoin.cpp

@@ -464,9 +464,7 @@ int GuiMain(int argc, char* argv[])
 
     // Generate high-dpi pixmaps
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
-#if QT_VERSION >= 0x050600
     QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
-#endif
 
 #if (QT_VERSION <= QT_VERSION_CHECK(5, 9, 8)) && defined(Q_OS_MACOS)
     const auto os_name = QSysInfo::prettyProductName();