Avoid adding image digest twice to tag on render

[yhrn]

Description

Avoid adding image digest twice to tag on render. This can happen when reading tags from file (--build-artifacts) where the tag already has a digest.

[codecov]

Codecov Report

Merging #5958 (d6bc64b) into master (20e00dc) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5958      +/-   ##
==========================================
+ Coverage   70.57%   70.63%   +0.06%     
==========================================
  Files         457      458       +1     
  Lines       17534    17612      +78     
==========================================
+ Hits        12374    12441      +67     
- Misses       4246     4253       +7     
- Partials      914      918       +4     

Impacted Files	Coverage Δ
pkg/skaffold/build/util.go	100.00% <100.00%> (ø)
pkg/skaffold/util/tar.go	50.66% <0.00%> (-5.34%)	⬇️
pkg/skaffold/inspect/types.go	100.00% <0.00%> (ø)
cmd/skaffold/app/cmd/inspect.go	100.00% <0.00%> (ø)
pkg/skaffold/inspect/buildEnv/modify_gcb.go	81.25% <0.00%> (ø)
pkg/skaffold/docker/parse.go	87.14% <0.00%> (+0.95%)	⬆️
cmd/skaffold/app/cmd/inspect_build_env.go	59.85% <0.00%> (+4.02%)	⬆️
pkg/skaffold/inspect/buildEnv/add_gcb.go	78.72% <0.00%> (+4.25%)	⬆️
pkg/skaffold/inspect/errors.go	56.09% <0.00%> (+56.09%)	⬆️

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