Cloning from sourceware.org fails in freetype2 project

We get failed build reports for freetype2. The build logs contain the following parts, which we believe are the reason for the error.

```
Step #3 - "compile-afl-address-x86_64": + git submodule update --init --depth 1 /src/freetype2-testing/external/bzip2
Step #3 - "compile-afl-address-x86_64": Submodule 'external/bzip2' (git://sourceware.org/git/bzip2.git) registered for path '../../../external/bzip2'
Step #3 - "compile-afl-address-x86_64": Cloning into '/src/freetype2-testing/external/bzip2'...
Step #3 - "compile-afl-address-x86_64": remote: Total 0 (delta 0), reused 0 (delta 0), pack-reused 0
Step #3 - "compile-afl-address-x86_64": error: Server does not allow request for unadvertised object 8ca1faa31f396d94ab927b257f3a05236c84e330
Step #3 - "compile-afl-address-x86_64": Fetched in submodule path '../../../external/bzip2', but it did not contain 8ca1faa31f396d94ab927b257f3a05236c84e330. Direct fetching of that commit failed.
```

However, this is not reproducible locally. The sourceware.org bzip2 checkout succeeds here.

Oss-fuzz reference bug reporting the build failure:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=51442#c4

The bug contains additional info on failed attempts at reproducing this.