CMake installation warning

```
CMake Warning at __build_clang/_deps/execution-src/cmake/beman-install-library.cmake:159 (message):
  beman_install_library(beman.execution): 'beman.execution' is not a target
Call Stack (most recent call first):
  __build_clang/_deps/execution-src/CMakeLists.txt:112 (beman_install_library)
```
Would probably be fixed by https://github.com/bemanproject/execution/issues/246.