fix: use https://git.savannah.gnu.org/git/bash instead of https://github.com/bolinfest/bash

[bolinfest]

Historically, we cloned the Bash repo from https://github.com/bminor/bash, but for whatever reason, it was removed at some point.

I had a local clone of it, so I pushed it to https://github.com/bolinfest/bash so that we could continue running our CI job. I did this in #9563, and as you can see, I did not tamper with the commit hash we used as the basis of this build.

Using a personal fork is not great, so this PR changes the CI job to use what appears to be considered the source of truth for Bash, which is https://git.savannah.gnu.org/git/bash.git.

Though in testing this out, it appears this Git server does not support the combination of git clone --depth 1 https://git.savannah.gnu.org/git/bash and git fetch --depth 1 origin a8a1c2fac029404d3f42cd39f5a20f24b6e4fe4b, as it fails with the following error:

error: Server does not allow request for unadvertised object a8a1c2fac029404d3f42cd39f5a20f24b6e4fe4b

so unfortunately this means that we have to do a full clone instead of a shallow clone in our CI jobs, which will be a bit slower.

Also updated codex-rs/shell-escalation/README.md to reflect this change.