apply code style script fails for multiple remote repositories (was ACTS-252)

Original author Christian Gumpert @cgumpert

The CI script for applying the code style fails if the branch is available in several remote repositories.

{noformat}

• git checkout jenkins_instructions error: pathspec 'jenkins_instructions' did not match any file(s) known to git. {noformat} Checking the list of available branches yields {noformat}atsjenkins@acts-ci:/mnt/jenkins/workspace/ACTS-MERGE$ sudo -u jenkins git branch -a

• (HEAD detached from origin/master) remotes/a-common-tracking-sw/ACTS-200_math_macros remotes/a-common-tracking-sw/ACTS-202_optimise_geometry_methods remotes/a-common-tracking-sw/ACTS-249_docker_images remotes/a-common-tracking-sw/ACTS-72_MaterialMapping remotes/a-common-tracking-sw/ACTSFW-6-12_Read_Sim_Digi_Adaptions remotes/a-common-tracking-sw/jenkins_instructions remotes/a-common-tracking-sw/master remotes/a-common-tracking-sw/release-0.01.X remotes/a-common-tracking-sw/release-0.02.X remotes/a-common-tracking-sw/release-0.03.X remotes/origin/ACTS-200_math_macros remotes/origin/ACTS-202_optimise_geometry_methods remotes/origin/ACTS-249_docker_images remotes/origin/ACTS-72_MaterialMapping remotes/origin/ACTSFW-6-12_Read_Sim_Digi_Adaptions remotes/origin/jenkins_instructions remotes/origin/master remotes/origin/release-0.01.X remotes/origin/release-0.02.X remotes/origin/release-0.03.X {noformat}

The script should be updated to explicitly checkout the branch from the source repository.