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.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: skottmckay <979079+skottmckay@users.noreply.github.com>

Author: Copilot

js/node/script/install.js

@@ -25,7 +25,7 @@ const INSTALL_METADATA = require('./install-metadata.js');
 
 // Bootstrap global-agent to honor the proxy settings in
 // environment variables, e.g. GLOBAL_AGENT_HTTPS_PROXY.
-// See https://github.com/gajus/global-agent/blob/v3.0.0/README.md#environment-variables for details.
+// See the https://github.com/gajus/global-agent ReadMe.md regarding environment variables.
 globalAgentBootstrap();
 
 // commandline flag:

js/scripts/utils.ts

@@ -8,7 +8,7 @@ import { JSZipObject } from 'jszip';
 
 // Bootstrap global-agent to honor the proxy settings in
 // environment variables, e.g. GLOBAL_AGENT_HTTPS_PROXY.
-// See https://github.com/gajus/global-agent/blob/v3.0.0/README.md#environment-variables for details.
+// See the https://github.com/gajus/global-agent ReadMe.md regarding environment variables.
 globalAgentBootstrap();
 
 export const downloadZip = async (url: string, maxRetryTimes = 3): Promise<Buffer> => {

js/web/script/pull-prebuilt-wasm-artifacts.ts

@@ -181,7 +181,7 @@ async function downloadArtifactsForRun(run: any): Promise<void> {
 async function main() {
   // Bootstrap global-agent to honor the proxy settings in
   // environment variables, e.g. GLOBAL_AGENT_HTTPS_PROXY.
-  // See https://github.com/gajus/global-agent/blob/v3.0.0/README.md#environment-variables for details.
+  // See the https://github.com/gajus/global-agent ReadMe.md regarding environment variables.
   globalAgentBootstrap();
 
   console.log(