Enable installation of pre-release packs

Since 2.11.3 pre-release packs have been ignored CodeQL when installing
packs. We re-enable this since we use pre-release packs internally (e.g.
in the common packs).

Author: lcartey

scripts/install-packs.py

@@ -18,6 +18,6 @@
 for pack in packs:
     pack_path = os.path.join(root, pack)
     # Run `codeql pack install` to install dependencies.
-    command = [args.codeql, 'pack', 'install', '--mode', args.mode, pack_path]
+    command = [args.codeql, 'pack', 'install', '--alow-prerelease', '--mode', args.mode, pack_path]
     print(f'Running `{" ".join(command)}`')
     subprocess.check_call(command)