guix: use glibc 2.31

Set minimum required glibc to 2.31.
The glibc 2.31 branch is still maintained:
https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/release/2.31/master.

Remove the stack-protector check from test-security-check, as the test
no-longer fails, and given the control we have of the end, the actual
security-check test seems sufficient (this might also be applied to some
of the other checks).

Drops runtime support for Ubuntu Bionic 18.04 and RHEL-8 from the release binaries.

doc/dependencies.md

@@ -19,7 +19,7 @@ You can find installation instructions in the `build-*.md` file for your platfor
 | --- | --- | --- | --- | --- |
 | [Boost](../depends/packages/boost.mk) | [link](https://www.boost.org/users/download/) | [1.81.0](https://github.com/bitcoin/bitcoin/pull/26557) | [1.73.0](https://github.com/bitcoin/bitcoin/pull/29066) | No |
 | [libevent](../depends/packages/libevent.mk) | [link](https://github.com/libevent/libevent/releases) | [2.1.12-stable](https://github.com/bitcoin/bitcoin/pull/21991) | [2.1.8](https://github.com/bitcoin/bitcoin/pull/24681) | No |
-| glibc | [link](https://www.gnu.org/software/libc/) | N/A | [2.27](https://github.com/bitcoin/bitcoin/pull/27029) | Yes |
+| glibc | [link](https://www.gnu.org/software/libc/) | N/A | [2.31](https://github.com/bitcoin/bitcoin/pull/29987) | Yes |
 | Linux Kernel | [link](https://www.kernel.org/) | N/A | [3.17.0](https://github.com/bitcoin/bitcoin/pull/27699) | Yes |
 
 ## Optional

doc/release-notes-29987.md

@@ -0,0 +1,6 @@
+Compatibility
+=============
+
+The minimum required glibc to run Bitcoin Core is now
+2.31. This means that RHEL 8 and Ubuntu 18.04 (Bionic)
+are no-longer supported. (#29987)