COMP: Fix CMP0177 install-path warning in WriteAnImage

The install(FILES ...) DESTINATION contained a doubled separator
("Code/Base//WriteAnImage"), and the install(TARGETS ...) DESTINATION
had a trailing slash. Under CMake 3.31+ (which enables CMP0177) the
unnormalized paths emit a developer warning, and the documentation and
python-superbuild dashboards treat any build warning as a failure, so
the gate fails for every PR built on a recent CMake.

Normalize both DESTINATION paths.

Author: hjmjohnson

src/IO/ImageBase/WriteAnImage/CMakeLists.txt

@@ -13,12 +13,12 @@ target_link_libraries(${PROJECT_NAME}
 )
 
 install(TARGETS ${PROJECT_NAME}
-  DESTINATION bin/ITKSphinxExamples/Base/
+  DESTINATION bin/ITKSphinxExamples/Base
   COMPONENT Runtime
 )
 
 install(FILES Code.cxx CMakeLists.txt
-  DESTINATION share/ITKSphinxExamples/Code/Base//WriteAnImage
+  DESTINATION share/ITKSphinxExamples/Code/Base/WriteAnImage
   COMPONENT Code
 )