Bundle lockfile is not generated on prefix on workspaces with no gem osdeps

[g-arjones]

This seems to have been the behavior since the early days, but it's unclear when it started to be a problem for workspaces that install gems from git sources and no gems osdeps.

Steps to reproduce:

1. Create an empty workspace:

$ mkdir ~/dev/test_ws
$ cd ~/dev/test_ws
$ wget https://github.com/rock-core/autoproj/raw/refs/heads/master/bin/autoproj_install
$ cat <<EOF > autoproj.gemfile
source "https://rubygems.org"
gem "autoproj", git: "https://github.com/rock-core/autoproj.git"
gem "autobuild", git: "https://github.com/rock-core/autobuild.git"
EOF
$ ruby autoproj_install --gemfile=autoproj.gemfile

2. Verify that the workspace is broken:

$ .autoproj/bin/autoproj exec ruby -e 'puts "foobar"'
The git source https://github.com/rock-core/autobuild.git is not yet checked out. Please run `bundle install` before trying to start your application
$ ls install/gems/Gemfile.lock 
ls: cannot access 'install/gems/Gemfile.lock': No such file or directory

3. Fix the workspace:

$ mkdir autoproj
$ echo "gem 'rubocop'" > autoproj/Gemfile
$ .autoproj/bin/autoproj osdeps
$ .autoproj/bin/autoproj exec ruby -e 'puts "foobar"'
foobar
$ ls install/gems/Gemfile.lock 
install/gems/Gemfile.lock

@doudou Any ideas?