Unable to locate `LocalPreferences.toml` outside of MPI.jl

I observe a strange behaviour using `MPI.jl#master` (0.20-dev) while running the `MPI.use_system_binary()` in a project outside of the MPI.jl project. Namely, the system MPI implementation seems to be correctly selected but the `LocalPreferences.toml` file that should be generated in the project is not there (only `Project.toml` and `Manifest.toml` are present). Do I miss something?

Reproducer:
```
[lraess@ault dev]$ mkdir tmp_test
[lraess@ault dev]$ cd tmp_test/
[lraess@ault dev]$ julia --project
_
_ _ _(_)_ | Documentation: https://docs.julialang.org
(_) | (_) (_) |
_ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 1.7.2 (2022-02-06)
_/ |\__'_|_|_|\__'_| | Official https://julialang.org/ release
|__/ |

julia>

(@v1.7) pkg> activate .
Activating new project at `/scratch/lraess/dev/tmp_test`

(tmp_test) pkg> add MPI#master

(tmp_test) pkg> st
Status `/scratch/lraess/dev/tmp_test/Project.toml`
[da04e1cc] MPI v0.20.0-dev `https://github.com/JuliaParallel/MPI.jl.git#master`

julia> using MPI

julia> MPI.use_system_binary()
┌ Info: MPI implementation
│ libmpi = "libmpi"
│ version_string = "Open MPI v4.0.6rc4, package: Open MPI root@ault08.cscs.ch Distribution, ident: 4.0.6rc4, repo rev: v4.0.6-33-gd71f8c2ba8, Unreleased developer copy\0"
│ impl = "OpenMPI"
│ version = v"4.0.6-rc4"
└ abi = "OpenMPI"
┌ Warning: The underlying MPI implementation has changed. You will need to restart Julia for this change to take effect
│ libmpi = "libmpi"
│ abi = "OpenMPI"
│ mpiexec = "mpiexec"
└ @ MPIPreferences ~/.julia/packages/MPIPreferences/uArzO/src/MPIPreferences.jl:119

shell> ls
Manifest.toml Project.toml

shell> cat Project.toml
[deps]
MPI = "da04e1cc-30fd-572f-bb4f-1f8673147195"

julia> exit()

[lraess@ault dev]$ julia --project
_
_ _ _(_)_ | Documentation: https://docs.julialang.org
(_) | (_) (_) |
_ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 1.7.2 (2022-02-06)
_/ |\__'_|_|_|\__'_| | Official https://julialang.org/ release
|__/ |

julia> using MPI

julia> MPI.MPI_LIBRARY_VERSION_STRING
"Open MPI v4.0.6rc4, package: Open MPI root@ault08.cscs.ch Distribution, ident: 4.0.6rc4, repo rev: v4.0.6-33-gd71f8c2ba8, Unreleased developer copy\0"
```