refactor: remove unnecessary nil check in RunContext

[Juneezee]

From the Go docs:

"For a nil slice, the number of iterations is 0" https://go.dev/ref/spec#For_range

Therefore, an additional nil check for job.RunsOn() before the loop is unnecessary because job.RunsOn() returns a []string. Example: https://go.dev/play/p/cmcRrMJ6Mb4

[codecov]

Codecov Report

Merging #1955 (5a2e6f6) into master (4989f44) will increase coverage by 0.90%.
Report is 220 commits behind head on master.
The diff coverage is 61.89%.

@@            Coverage Diff             @@
##           master    #1955      +/-   ##
==========================================
+ Coverage   61.22%   62.13%   +0.90%     
==========================================
  Files          46       52       +6     
  Lines        7141     8487    +1346     
==========================================
+ Hits         4372     5273     +901     
- Misses       2462     2795     +333     
- Partials      307      419     +112     

Files Changed	Coverage Δ
pkg/common/outbound_ip.go	0.00% <0.00%> (ø)
pkg/container/docker_cli.go	82.23% <ø> (ø)
pkg/container/docker_logger.go	52.08% <ø> (ø)
pkg/container/docker_volume.go	0.00% <0.00%> (ø)
pkg/container/file_collector.go	39.68% <0.00%> (+2.38%)	⬆️
pkg/container/host_environment.go	0.00% <0.00%> (ø)
...ontainer/linux_container_environment_extensions.go	23.07% <0.00%> (-1.25%)	⬇️
pkg/container/util.go	0.00% <0.00%> (ø)
pkg/exprparser/functions.go	66.32% <0.00%> (-1.04%)	⬇️
pkg/container/docker_run.go	13.45% <7.14%> (-0.13%)	⬇️
... and 29 more

... and 2 files with indirect coverage changes

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