Only allow 1 or 2 "New version" PR(s) per package to be open at a time, to reduce the PR backlog.

The PR backlogs in this repo tend to be crowded (which I can attest to), so one possible way to shorten them would be to simply just allow 1 or 2 version update PRs per package to be open at any given time.

Examples of the situations I'm thinking of, in this list ones with ≥5 open:
* OpenCLICollective.gro - https://github.com/microsoft/winget-pkgs/pulls?q=is%3Apr+is%3Aopen+OpenCLICollective.gro (8 open)
* Speakeasy.speakeasy - https://github.com/microsoft/winget-pkgs/pulls?q=is%3Apr+is%3Aopen+Speakeasy.speakeasy (8 open)
* CumulusMX.CumulusMX - https://github.com/microsoft/winget-pkgs/pulls?q=is%3Apr+is%3Aopen+CumulusMX.CumulusMX (6 open)
* LuisPater.CLIProxyAPI - https://github.com/microsoft/winget-pkgs/pulls?q=is%3Apr+is%3Aopen+luispater.cliproxyapi (6 open)

In the event of there being more version update PRs than allowed, the PRs for the oldest version(s) among them are the ones who should be closed.

Start with the four linked GitHub PR searches and the nine-comment issue discussion to understand the backlog pattern and the proposed limit. Identify where version-update PRs are created or managed; done means enforcing a one- or two-PR-per-package limit and closing the oldest excess PRs.

Written by the indexing model from the issue text.