[pipeline/trusted-resources] Refact/clean error on return vals

[austinzhao-go]

Changes

Refactor the helper func getSignerFromFile to remove the unused error return val

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• Includes docs (if user facing) - not user facing as for refactoring work
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[austinzhao-go]

/hold

till #886 got merged

[austinzhao-go]

/assign @Yongxuanzhang @wlynch

[wlynch]

/lgtm

I think this looks good, but waiting until the base commit is submitted before approving. (alternatively if you want to cherry pick the commit that works for me too)

[austinzhao-go]

/unhold

as #886 was merged

[Yongxuanzhang]

Thanks a lot @austinzhao-go and @wlynch !! 😄

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Yongxuanzhang

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[Yongxuanzhang]

/lgtm

[austinzhao-go]

thanks @Yongxuanzhang