build: Fix duplicate "browser_connected" debug log message

When there is a retry after a timeout, the final "browser_connected"
debug message was logged multiple times.

Example:

```
05:30:49 [qtap_browser_client_S1_C1_edge] browser_spawn_command /usr/bin/microsoft-edge …

05:31:49 [qtap_browser_client_S1_C1_edge] WARNING browser_connect_timeout Browser did not start within 60s
05:31:49 qtap_server_S1] browser_connect_retry Retrying, attempt 2 of 3
05:31:49 [qtap_browser_client_S1_C1_edge] browser_spawn_command /usr/bin/microsoft-edge
05:31:49 [qtap_browser_client_S1_C1_edge] browser_launch_stopped BrowserConnectTimeout: Browser did not start within 60s
05:31:49 [qtap_browser_client_S1_C1_edge] browser_connected Edge Headless connected! Serving test file.
05:31:49 [qtap_browser_client_S1_C1_edge] browser_connected Edge Headless connected! Serving test file.
05:31:49 [qtap_browser_client_S1_C1_edge] WARNING browser_idle_timeout Test timed out after 60s
```

This happened because the first attempt was still listening to the `clientonline`
event and handling the later attempt to send its own copy of the log message
just before calling `resolve()` on the already-rejected Promise.

That resolve() call is a no-op, but logger call is not.

We could fix this by carefully avoiding that through local state, such as by
setting `connectTimeoutTimer = false` from the setTimeout callback and checking
that in the 'clientonline' callback. Or, by adding support for `eventbus.off()`
and removing the 'clientonline' callback from inside setTimeout callback.

This patch does none of that, and instead leverages the fact that the Promise
boundary already cleanly represents this, by moving the log message to the
caller.

Author: Krinkle

src/server.js

@@ -444,6 +444,7 @@ class ControlServer {
 
       try {
         await this.launchBrowserAndConnect(browserFn, browser, signals);
+        logger.debug('browser_connected', `${browser.getDisplayName()} connected! Serving test file.`);
       } catch (e) {
         // Handle util.BrowserConnectTimeout from launchBrowserAndConnect
         //
@@ -538,9 +539,7 @@ class ControlServer {
       })
       .catch(/** @type {Error|Object|string} */ e => {
         // Silence any errors from browserFn that happen after we called browser.stop().
-        if (signals.browser.aborted) {
-          browser.logger.debug('browser_launch_stopped', String(e.cause || e));
-        } else {
+        if (!signals.browser.aborted) {
           browser.logger.warning('browser_launch_error', e);
           browser.stop(e);
           throw e;
@@ -574,7 +573,6 @@ class ControlServer {
         this.eventbus.on('clientonline', (event) => {
           if (event.clientId === browser.clientId) {
             clearTimeout(connectTimeoutTimer);
-            browser.logger.debug('browser_connected', `${browser.getDisplayName()} connected! Serving test file.`);
             resolve(null);
           }
         });