Rust e2e: align in-process host auth token with the mock's registered user

In-process, the SDK github_token (lowered to --auth-token-env COPILOT_SDK_AUTH_TOKEN
for the spawned child) is not passed to the worker, so host-side auth resolves from
GH_TOKEN/GITHUB_TOKEN. The InProcessEnvGuard set these to a placeholder the replay
mock never registered, so auth resolved as unauthenticated (client::should_get_
authenticated_status / should_list_models_when_authenticated) or hit real GitHub.
Use DEFAULT_TEST_TOKEN — the token set_default_copilot_user registers as the
authenticated Copilot user — so in-process auth matches the mock. Fixes the two
client auth tests and callback_token_is_applied_as_authorization_header in-process.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

rust/tests/e2e/support.rs

@@ -608,8 +608,14 @@ impl InProcessEnvGuard {
             return None;
         }
         let mut pairs: Vec<(OsString, OsString)> = ctx.environment();
-        pairs.push(("GH_TOKEN".into(), "fake-token-for-e2e-tests".into()));
-        pairs.push(("GITHUB_TOKEN".into(), "fake-token-for-e2e-tests".into()));
+        // In-process, the SDK's `github_token` (lowered to `--auth-token-env
+        // COPILOT_SDK_AUTH_TOKEN` for the spawned child) is not passed to the worker,
+        // so host-side auth resolves from GH_TOKEN/GITHUB_TOKEN instead. Use the same
+        // token the replay mock registers as the authenticated Copilot user
+        // (`set_default_copilot_user` → DEFAULT_TEST_TOKEN); a placeholder token the
+        // mock doesn't know would resolve as unauthenticated (or hit real GitHub).
+        pairs.push(("GH_TOKEN".into(), DEFAULT_TEST_TOKEN.into()));
+        pairs.push(("GITHUB_TOKEN".into(), DEFAULT_TEST_TOKEN.into()));
 
         let mut saved: Vec<(OsString, Option<OsString>)> = Vec::new();
         for (key, value) in &pairs {