fix(upgrade-tests): redirect stdout of docker pull in upgrade tests (#11643)

[hanshuebner]

Summary

This seems to have creeped into all branches and is needed for the upgrade tests to pass.

Checklist

• The Pull Request has tests
• A changelog file has been added to CHANGELOG/unreleased/kong or adding skip-changelog label on PR if unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

[team-gateway-bot]

The backport to release/3.2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-release/3.2.x release/3.2.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.2.x
# Create a new branch
git switch --create backport-11653-to-release/3.2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 5eb4c0dd552a2450e9f39c816477efe5eba183d9
# Push it to GitHub
git push --set-upstream origin backport-11653-to-release/3.2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.2.x

Then, create a pull request where the base branch is release/3.2.x and the compare/head branch is backport-11653-to-release/3.2.x.