Adapter Code Coverage workflow: Support Go version upgrades

[anishb-ms]

## Problem

The `adapter-code-coverage.yml` workflow currently installs Go before checking out PR code:

```yaml
steps:
  - name: Install Go
    uses: actions/setup-go@v5
    with:
      go-version: 1.24.0       # hardcoded

  - name: Checkout Code        # PR code checked out after

Since this workflow uses pull_request_target, GitHub always runs the master branch's version of the workflow file. This means any PR that upgrades the Go version in go.mod will fail because:

1. Master installs Go 1.24.0
2. PR's go.mod declares a newer Go version (e.g., go 1.25 or go 1.26)
3. At build time, Go 1.24.0 auto-downloads the newer toolchain — but auto-downloaded toolchains are lightweight bundles missing the covdata tool
4. Tests fail with: go: no such tool "covdata"

This makes it impossible to upgrade Go via a PR — the adapter coverage check will always block it.

Fix
Swap the step order and use go-version-file to dynamically read the Go version from the checked-out PR code:

  steps:
  - name: Checkout Code        # checkout FIRST
    uses: actions/checkout@v4
    ...

  - name: Install Go           # then install based on go.mod
    uses: actions/setup-go@v5
    with:
      go-version-file: go.mod

This ensures actions/setup-go performs a full installation of whatever Go version the PR requires — no auto-download, no missing tools, no version mismatch.

Impact

• Zero risk for current PRs: master's go.mod declares go 1.23.0, so setup-go installs 1.23.x — same behavior as today.

• Unblocks future Go upgrades: version upgrades will work automatically without needing to update this workflow.