$ nproc
16
$ cd Example.jl
$ echo '@show Threads.nthreads()' >> test/runtests.jl
$ rm -f Manifest.toml
$ julia +1.11 --project --eval 'using Pkg; Pkg.test(; julia_args = ["--threads=auto"])'
...
Testing Running tests...
Threads.nthreads() = 16
$ rm -f Manifest.toml
$ julia +1.12 --project --eval 'using Pkg; Pkg.test(; julia_args = ["--threads=auto"])'
...
Testing Running tests...
Threads.nthreads() = 1