Make the bot/bot-check.sh script correctly pick up builds for accelerators

[bedroge]

Fixes EESSI/eessi-bot-software-layer#286 (more or less). The problem here was that the script was only checking for new installations in the CPU prefix, and it interpreted everything else (including stuff in the accelerator prefix) to be "other files". The latter would get printed in full, leading to a very large Github comment. This is now fixed by appending accel/${accelerator} to ${prefix} for accelerator builds. Note that this only works for non-mixed builds (i.e. either CPU-only builds or GPU-only builds), but I think we decided that we would not allow this, at least not for now, to prevent that things get mixed up.

[eessi-bot]

Instance eessi-bot-mc-aws is configured to build for:

• architectures: x86_64/generic, x86_64/intel/haswell, x86_64/intel/skylake_avx512, x86_64/amd/zen2, x86_64/amd/zen3, aarch64/generic, aarch64/neoverse_n1, aarch64/neoverse_v1
• repositories: eessi.io-2023.06-compat, eessi-hpc.org-2023.06-software, eessi-hpc.org-2023.06-compat, eessi.io-2023.06-software

[eessi-build-deploy-bot-deucalion]

Instance boegel-bot-deucalion is configured to build for:

• architectures: aarch64/a64fx
• repositories: eessi.io-2023.06-software

[eessi-bot]

Instance eessi-bot-mc-azure is configured to build for:

• architectures: x86_64/amd/zen4
• repositories: eessi-hpc.org-2023.06-software, eessi-hpc.org-2023.06-compat, eessi.io-2023.06-software, eessi.io-2023.06-compat

[bedroge]

Successfully tested in #728 (comment).