pico-env.ps1 tries to set up wrong env. variables

[daniol]

The script pico-env.ps1 reads the output from pico-env.cmd and sets the environment variables without validation.

This script has currently two problems:

• It also set environment variables with the process messages of the VerifyExe step, for example it sets the following environment variables:
  'Checking "GNU Arm Embedded Toolchain"...' to ''
  'Checking "CMake"...' to ''
  'Checking "Ninja"...' to ''
  'Checking "Python 3"...' to ''
  'Checking "Git"...' to ''
• In some scenarios the script pico-env.cmd outputs an additional empty line at the end, this way pico-env.ps1 tries to set an environment variable with an empty name, which causes an error. This seems to happen only when it is run inside a SYSTEM service (for example, when it is called inside a Gitlab Runner job).

[daniol]

Fixed with #51