fix: incorrect generated image tag for bentoctl

[jjmachan]

Description

Motivation and Context

How Has This Been Tested?

Checklist:

• My code follows the bentoctl code style, both make format and
  make lint script have passed
• My change reduces project test coverage and requires unit tests to be added
• I have added unit tests covering my code change
• My change requires a change to the documentation
• I have updated the documentation accordingly

[codecov]

Codecov Report

Merging #122 (1c1c74c) into main (18c6b86) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #122   +/-   ##
=======================================
  Coverage   39.71%   39.71%           
=======================================
  Files          15       15           
  Lines         851      851           
=======================================
  Hits          338      338           
  Misses        513      513           

Flag	Coverage Δ
unit-tests	39.71% <ø> (ø)

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Impacted Files	Coverage Δ
bentoctl/deployment_config.py	62.87% <ø> (ø)

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