[GUI] Add missing include

[AjinkyaDahale]

This memory header is needed for unique_ptr, at least on Manjaro/Arch Linux with GCC.

[AjinkyaDahale]

@adrianinsaval please confirm if current master was building or not, and if this change improves the situation.

[adrianinsaval]

current master fails for me too, but I still haven't got a chance to test your PR

[4023/4170] Building CXX object src/Mod/Test/Gui/CMakeFiles/QtUnitGui.dir/AppTestGui.cpp.o
FAILED: src/Mod/Test/Gui/CMakeFiles/QtUnitGui.dir/AppTestGui.cpp.o 
/usr/sbin/ccache /usr/lib/ccache/bin/c++ -DBOOST_ATOMIC_DYN_LINK -DBOOST_ATOMIC_NO_LIB -DBOOST_DATE_TIME_DYN_LINK -DBOOST_DATE_TIME_NO_LIB -DBOOST_FILESYSTEM_DYN_LINK -DBOOST_FILESYSTEM_NO_LIB -DBOOST_PROGRAM_OPTIONS_DYN_LINK -DBOOST_PROGRAM_OPTIONS_NO_LIB -DBOOST_REGEX_DYN_LINK -DBOOST_REGEX_NO_LIB -DBOOST_SYSTEM_DYN_LINK -DBOOST_SYSTEM_NO_LIB -DBOOST_THREAD_DYN_LINK -DBOOST_THREAD_NO_LIB -DHAVE_CONFIG_H -DPYCXX_6_2_COMPATIBILITY -DPYSIDE_QML_SUPPORT=1 -DQT_CORE_LIB -DQT_GUI_LIB -DQT_NETWORK_LIB -DQT_NO_DEBUG -DQT_OPENGL_LIB -DQT_PRINTSUPPORT_LIB -DQT_SVG_LIB -DQT_UITOOLS_LIB -DQT_WIDGETS_LIB -DQT_XML_LIB -DQtUnitGui_EXPORTS -D_OCC64 -I/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/build/src/Mod/Test/Gui/QtUnitGui_autogen/include -I/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/build -I/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/build/src -I/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/src -I/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/build/src/Mod/Test/Gui -isystem /usr/include/python3.10 -isystem /usr/include/qt -isystem /usr/include/qt/QtCore -isystem /usr/lib/qt/mkspecs/linux-g++ -isystem /usr/include/qt/QtXml -isystem /usr/include/qt/QtWidgets -isystem /usr/include/qt/QtGui -isystem /usr/include/qt/QtOpenGL -isystem /usr/include/qt/QtPrintSupport -isystem /usr/include/qt/QtSvg -isystem /usr/include/qt/QtNetwork -isystem /usr/include/qt/QtUiTools -isystem /usr/include/shiboken2 -isystem /usr/include/PySide2 -Wall -Wextra -Wno-write-strings -march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions         -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security         -fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSERTIONS -fPIC -w -fPIC -fPIC -std=gnu++17 -MD -MT src/Mod/Test/Gui/CMakeFiles/QtUnitGui.dir/AppTestGui.cpp.o -MF src/Mod/Test/Gui/CMakeFiles/QtUnitGui.dir/AppTestGui.cpp.o.d -o src/Mod/Test/Gui/CMakeFiles/QtUnitGui.dir/AppTestGui.cpp.o -c /__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/src/Mod/Test/Gui/AppTestGui.cpp
In file included from /__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/src/Mod/Test/Gui/AppTestGui.cpp:28:
/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/src/Gui/Language/Translator.h:94:10: error: ‘unique_ptr’ in namespace ‘std’ does not name a template type
   94 |     std::unique_ptr<Translator, std::function<void(Translator*)>> decimalPointConverter;
      |          ^~~~~~~~~~
/__w/pacman-repo/pacman-repo/PKGBUILD/freecad-git/src/FreeCAD/src/Gui/Language/Translator.h:27:1: note: ‘std::unique_ptr’ is defined in header ‘<memory>’; did you forget to ‘#include <memory>’?
   26 | #include <QObject>
  +++ |+#include <memory>
   27 | #include <list>

but that is the suggested fix, I had encountered a problem like this before too when testing a PR: #3062 (comment)