Fix shell executor

[cplee]

Issue #, if available:

Description of changes:

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[github-actions]

Package	Line Rate	Complexity	Health
github.com/aws/codecatalyst-runner-cli/codecatalyst-runner/cmd	68%	0	✔
github.com/aws/codecatalyst-runner-cli/codecatalyst-runner/pkg/actions	76%	0	✔
github.com/aws/codecatalyst-runner-cli/codecatalyst-runner/pkg/workflows	63%	0	✔
github.com/aws/codecatalyst-runner-cli/command-runner/internal/containers/docker	15%	0	❌
github.com/aws/codecatalyst-runner-cli/command-runner/internal/fs	31%	0	❌
github.com/aws/codecatalyst-runner-cli/command-runner/pkg/common	72%	0	✔
github.com/aws/codecatalyst-runner-cli/command-runner/pkg/features	51%	0	➖
github.com/aws/codecatalyst-runner-cli/command-runner/pkg/runner	60%	0	➖
Summary	50% (1675 / 3373)	0	➖

Minimum allowed line rate is 48%