Sync eng/tools/js-sdk-release-tools to @azure-tools/js-sdk-release-tools@2.16.8 (#38616)

Syncs `eng/tools/js-sdk-release-tools` with
[azure-sdk-tools#15621](Azure/azure-sdk-tools#15621),
bumping `@azure-tools/js-sdk-release-tools` from `2.16.7` → `2.16.8`.

### Packages impacted by this PR
`eng/tools/js-sdk-release-tools`

### Issues associated with this PR
Sync with azure-sdk-tools PR #15621

### Describe the problem that is addressed by this PR
The local `eng/tools/js-sdk-release-tools` wrapper was pinned to
`@azure-tools/js-sdk-release-tools@2.16.7`. This PR brings it up to
`2.16.8`, which includes:
- README update support in `generateAzureSDKPackage`
- `tryBuildSamples` treats `SpecPullRequest` mode as a release (improved
error handling)
- Enhanced changelog content for first-release and modular client
migration scenarios
- Improved model-only checker for beta releases + Git tag verification
- Dependency bumps: `fast-uri`, `simple-git`, `vite`, `ip-address`,
`socks`
- Prettier enabled for the tooling source

### What are the possible designs available to address the problem? If
there are more than one possible design, why was the one in this PR
chosen?
N/A — version pin update.

### Are there test cases added in this PR? _(If not, why?)_
No. This is a dependency version bump; test coverage lives in the
upstream `azure-sdk-tools` repo.

### Provide a list of related PRs _(if any)_
- Azure/azure-sdk-tools#15621

### Checklists
- [ ] Added impacted package name to the issue description.
- [ ] Does this PR need any fixes in the SDK Generator?** _(If so,
create an Issue in the
[Autorest/typescript](https://github.com/Azure/autorest.typescript)
repository and link it here.)_
- [ ] Added a changelog (if necessary).

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: skywing918 <41712999+skywing918@users.noreply.github.com>

Author: Copilot

eng/tools/js-sdk-release-tools/package-lock.json

@@ -1,5 +1,5 @@
 {
   "dependencies": {
-    "@azure-tools/js-sdk-release-tools": "2.16.7"
+    "@azure-tools/js-sdk-release-tools": "2.16.8"
   }
 }