fix: Use gcloud spec pool instead of deprecated WorkerPool

[tejal29]

The field WorkerPool is deprecated since v0.50.0 in CloudBuild API
https://github.com/googleapis/google-api-go-client/blob/v0.58.0/cloudbuild/v1alpha1/cloudbuild-gen.go#L744

Switching to PoolOption in the Cloud Build Spec.

[codecov]

Codecov Report

Merging #6658 (7f8bcf4) into main (290280e) will decrease coverage by 0.49%.
The diff coverage is 53.33%.

@@            Coverage Diff             @@
##             main    #6658      +/-   ##
==========================================
- Coverage   70.48%   69.99%   -0.50%     
==========================================
  Files         515      522       +7     
  Lines       23150    23740     +590     
==========================================
+ Hits        16317    16616     +299     
- Misses       5776     6039     +263     
- Partials     1057     1085      +28     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	89.00% <0.00%> (-1.82%)	⬇️
cmd/skaffold/skaffold.go	0.00% <ø> (ø)
pkg/diag/recommender/container_errors.go	0.00% <0.00%> (ø)
pkg/diag/validator/pod.go	1.32% <0.00%> (ø)
pkg/skaffold/build/buildpacks/logger.go	0.00% <ø> (ø)
pkg/skaffold/build/cluster/logs.go	0.00% <ø> (-16.67%)	⬇️
cmd/skaffold/app/cmd/cmd.go	70.32% <66.66%> (-0.73%)	⬇️
pkg/diag/validator/resource.go	47.05% <66.66%> (ø)
pkg/skaffold/build/docker/docker.go	86.44% <66.66%> (-2.85%)	⬇️
pkg/skaffold/build/docker/errors.go	63.33% <80.00%> (-2.23%)	⬇️
... and 79 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 26dc1b8...7f8bcf4. Read the comment docs.