Document any delay of moving selector caches (eg. `runtime: node@lts`) after release of new versions

[karlhorky]

actions/setup-node has significant delays (up to 1 month!) of lts/* aliases (cache invalidation bug), due to slow updates in actions/runner-images:

• Security: lts/* installs old LTS versions up to 1 month+ after release actions/setup-node#1236
• older issue, with a few more details: Security: lts/* installs old LTS versions up to 1 month+ after release actions/setup-node#1236

Does pnpm/setup also suffer from the same delays due to caching? I noticed this wording, which sounds familiar to the explanations by the actions/setup-node team:

a moving selector such as node@lts is reported and cached under the version it resolved to

setup/src/install-runtime/index.ts

Lines 61 to 64 in 703c526

	/**
	* Read the versions `pnpm runtime set` actually installed, so that a moving
	* selector such as `node@lts` is reported and cached under the version it
	* resolved to. One listing covers every runtime, so this stays a single

If there are any delays, these should be documented.

But if pnpm/setup does not suffer from cache invalidation problems like the actions/setup-node problem, then I would propose it also in those two issues above as an alternative to actions/setup-node.