Investigate replacement of npm commands by pnpm on Github Actions

[diofeher]

Currently our pipeline is being setup using npm, but our repository manager is set to pnpm.

https://pnpm.io/continuous-integration#github-actions

https://github.com/opentofu/registry-ui/blob/main/.github/workflows/verify.yml#L63

Investigate if it's necessary to replace these commands by pnpm and what would be the difference between using them.

[diofeher]

This was noticed by analyzing the comments on this PR. #296