remove CI build using lalsuite-dev-gcc:8 replace with build on Buster

Description

This removes the CI build using igwn/lalsuite-dev/gcc:8 as this is based on gcc:8 and that container is no longer supported. This also replaces the top-level build on Bullseye with a build using Buster, the package level build has been running on Bullseye for some time so there is no need for a separate top-level build using this OS. Buster is now used as the default compiler on Buster is gcc-8.3.0 so this fills the gap by the remove build using igwn/lalsuite-dev-gcc:8.

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

Please provide details on any reviews related to this change and and the associated reviewers.