SLURM: the project option should override the WCKey environment variable

Using the new project option added by commit 76b89a67, one is able to specify the SLURM WCKey (or project name) of an HPC job.

However, this key is set through the batch script file (HPC_STDIN) but, as per SLURM documentation, setting the WCKey through the batch script does not override the key which might have already been set using the SBTACH_WCKEY environment variable (https://slurm.schedmd.com/sbatch.html):

NOTE: Environment variables will override any options set in a batch script, and command line options will override any environment variables.

As such, the project name should be set in the hpc_runcode option instead of the hpc_stdin one.