test: use native pnpm install for pnpm workspace example

[MikeMcC399]

• closes Renovate PRs failing in example-start-and-pnpm-workspaces #1594
• closes PNPM Workspace example - erroneous for mono-repo setups #1590

Situation

• The example-start-and-pnpm-workspaces may fail under certain re-run conditions if the Cypress binary cache has been evicted (see Renovate PRs failing in example-start-and-pnpm-workspaces #1594 for full details). The failure message is:

  /usr/local/bin/npx cypress verify
  The cypress npm package is installed, but the Cypress binary is missing.
  

• The action does not cache the pnpm store, and instead caches the .npm cache. It also uses uses npx commands (see feature request Package manager caching strategy for pnpm and Yarn Modern #1366).

• The action is not aware of pnpm workspaces (see feature request Add workspace support for pnpm #1144) and so cannot reliably install and cache dependencies on its own.

• Additionally, issue PNPM Workspace example - erroneous for mono-repo setups #1590 reported problems using the example in a monorepo. It should be clear that the example is a workaround only and does not represent full support of pnpm workspaces.

Change

Replace dependency installation in example-start-and-pnpm-workspaces, currently using the action, to instead use a direct call to:

pnpm install --frozen-lockfile

Update the README > pnpm workspaces documentation section accordingly.

Verification

Run and re-run the workflow example-start-and-pnpm-workspaces

Examine the logs for the PR and note that there are no caches used, so they can no longer get out of sync.

[cypress-app-bot]

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[github-actions]

🎉 This PR is included in version 6.10.5 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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