fix: include var name into tracing error message (#779) (#780)

playwright/src/main/java/com/microsoft/playwright/impl/TracingImpl.java

@@ -93,7 +93,7 @@ class TracingImpl implements Tracing {
     includeSources = options.sources != null;
     if (includeSources) {
       if (!context.connection.isCollectingStacks()) {
-        throw new PlaywrightException("Source root directories must be provided to enable source collection");
+        throw new PlaywrightException("Source root directory must be specified via PLAYWRIGHT_JAVA_SRC environment variable when source collection is enabled");
       }
       params.addProperty("sources", true);
     }