Remove usages of "new" as variable name

[SaschaSchwarze0]

Changes

Golangci-lint started to complain the usage of new as variable name: https://github.com/shipwright-io/build/actions/runs/11785633189/job/32827274452?pr=1730

  Running [/home/runner/golangci-lint-1.62.0-linux-amd64/golangci-lint run --path-prefix=go/src/github.com/shipwright-io/build --timeout=10m] in [/home/runner/work/build/build/go/src/github.com/shipwright-io/build] ...
  Error: go/src/github.com/shipwright-io/build/pkg/env/env.go:17:19: redefines-builtin-id: redefinition of the built-in function new (revive)
  func MergeEnvVars(new []corev1.EnvVar, into []corev1.EnvVar, overwriteValues bool) ([]corev1.EnvVar, error) {
                    ^
  Error: go/src/github.com/shipwright-io/build/pkg/volumes/volumes.go:72:65: redefines-builtin-id: redefinition of the built-in function new (revive)
  func MergeBuildVolumes(into []buildv1beta1.BuildStrategyVolume, new []buildv1beta1.BuildVolume) ([]buildv1beta1.BuildStrategyVolume, error) {

I am renaming those two.

Submitter Checklist

• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
• Set a kind label on this PR
• Release notes block has been filled in, or marked NONE

Release Notes

NONE

[qu1queee]

/lgtm
/approve

[openshift-ci]

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