Update global-agent comments to use version-agnostic GitHub URL (#28061)
### Description
Updates the `global-agent` reference in code comments across three files
to use a version-agnostic GitHub repository URL, so the comments won't
need updating on future version bumps.
- **`js/scripts/utils.ts`** — replace version-specific blob URL with `//
See the https://github.com/gajus/global-agent ReadMe.md regarding
environment variables.`
- **`js/node/script/install.js`** — same update
- **`js/web/script/pull-prebuilt-wasm-artifacts.ts`** — same update
### Motivation and Context
The actual `global-agent` dependency version bump (from `^3.0.0` to
`^4.1.3`) was done in #27838. The accompanying comments referenced a
version-specific blob URL
(`/blob/v4.1.3/README.md#environment-variables`) which would need
updating on every future version bump. Switching to the top-level
repository URL keeps the comments accurate regardless of which version
is installed.
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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: skottmckay <979079+skottmckay@users.noreply.github.com>