Sandbox swiftshader_spvtools_update_build_version

Sandboxing produces this diff:
  1c1
  < "v2023.2", "SPIRV-Tools v2023.2 android-u-beta-1-gpl-587-g9d167f845"
  ---
  > "v2023.2", "SPIRV-Tools v2023.2 unknown hash, 2023-11-30T17:54:23"

But the git repository is already not garunteed to exist on CI, and
the genrule is consequently commented with a FIXME about that.

Bug: 307824623
Test: ./build/soong/tests/genrule_sandbox_test.py swiftshader_spvtools_update_build_version
Change-Id: I98e65781bd49137662ed020927940b0f3e4d645b