ARM-CI: Prevent creation of job for Checked configuration

ARM-CI: Prevent creation of job for Checked configuration

Previously we checked if the configuration being built is either of Debug or Release
after the job had already been created. This resulted in a job being created for
Checked configuration with no commands to execute (for this job).
We prevent the unnecessary creation of job for the Checked configuration by
returning control at the very beginning of the <LinuxARMEmulator, arm, Checked> iteration

Signed-off-by: Prajwal A N <an.prajwal@samsung.com>
Commit migrated from https://github.com/dotnet/coreclr/commit/bb4009985fb4ee694d9920539301d6b8bed2ead1