pimcommonakonadi/designer/CMakeLists.txt - dedupe OUTPUT_NAME

fixes:
ninja: error: build.ninja:6440: multiple rules generate
bin/pimcommonwidgets.so [-w dupbuild=err]
2 jobs for master in 11 minutes and 22 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #51761
build_clazy_clang_tidy

00:11:21

passed #51760
linux kf5-qt5 qt5.12

00:09:07

45.0%