Enable `pyfakefs` in bp2build

`//tools/asuite/atest:java-test-filter-generator-test` requires this
dependency.

Test: presubmit
Bug: 301180123
Change-Id: I9ed0d1a89b34a985c671960546914c039e4e4556
diff --git a/android/allowlists/allowlists.go b/android/allowlists/allowlists.go
index 5354611..eb34cad 100644
--- a/android/allowlists/allowlists.go
+++ b/android/allowlists/allowlists.go
@@ -203,6 +203,7 @@
 		"external/pcre":                          Bp2BuildDefaultTrueRecursively,
 		"external/perfmark/api":                  Bp2BuildDefaultTrueRecursively,
 		"external/protobuf":                      Bp2BuildDefaultTrueRecursively,
+		"external/python/pyfakefs/pyfakefs":      Bp2BuildDefaultTrueRecursively,
 		"external/python/pyyaml/lib/yaml":        Bp2BuildDefaultTrueRecursively,
 		"external/python/six":                    Bp2BuildDefaultTrueRecursively,
 		"external/python/jinja/src":              Bp2BuildDefaultTrueRecursively,