Fix integration test to properly demonstrate package exclusion bug

The test was extracting from the entire workspace, which caused both
modules to be treated as input packages. This meant their ModDirs were
added to wantedRoots even without the fix, so the bug never manifested.

Changed test.py to extract only mainmodule packages using a specific
command pattern. This ensures:
- Only mainmodule is in the initial input packages
- configmodule is visited as a dependency
- Without the fix, configmodule's ModDir is NOT in wantedRoots
- The relative path check produces ".." and incorrectly excludes it

Test results:
- WITHOUT fix: 2 files extracted (configmodule missing) ❌
- WITH fix: 4 files extracted (all present) ✅

This addresses the reviewer's feedback that the test was passing
without any code changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: allsmog

go/ql/integration-tests/package-exclusion-fix/test.py

@@ -15,4 +15,6 @@
 #
 # Fix: Adds all dependency ModDirs to wantedRoots and prioritizes checking them first.
 def test(codeql, go):
-    codeql.database.create(source_root="src")
+    # Extract only mainmodule packages to reproduce the bug scenario
+    # Without the fix, configmodule won't be in wantedRoots and will be excluded
+    codeql.database.create(command=["go", "list", "./mainmodule/..."], source_root="src")