fix: shellcheck source for env vars

1 job for main in 30 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Test
failed shellcheck #24
container

00:00:30

 
Name Stage Failure
failed
shellcheck Test There has been a runner system failure, please try again
In ./mangle/validate_repos line 8:
source "$(dirname "$0")/../sync/common"
^-- SC1091: Not following: ../sync/common was not specified as input (see shellcheck -x).

For more information:
https://www.shellcheck.net/wiki/SC1091 -- Not following: ../sync/common was...
Cleaning up file based variables
Running cleanup_file_variables in runner helper
ERROR: Job failed (system failure): exit status 2