Add GCC 12 and HIP 6 CI configuration

[msimberg]

Fixes #1164. The newly added GCC 12/HIP 6 configuration is now run on pushes and replaces the old GCC 12/HIP 5 which is still run on merges.

GCC (libstdc++) 13 and newer are incompatible with HIP for now: https://github.com/spack/spack/pull/46291.

[codacy-production[bot]]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
:white_check_mark: +0.00% (target: -1.00%)	:white_check_mark: ∅ (target: 90.00%)

Coverage variation details

| | Coverable lines | Covered lines | Coverage | | ------------- | ------------- | ------------- | ------------- | | Common ancestor commit (ad29ce30a29f11c794d29dfb2c8c0cc96ddb66ae) | 18358 | 13717 | 74.72% | | | Head commit (b36003f2a2ee52b38c3c110a88cba747e0b6cc5c) | 18358 (+0) | 13717 (+0) | 74.72% (**+0.00%**) | **Coverage variation** is the difference between the coverage for the head and common ancestor commits of the pull request branch: ` - `

Diff coverage details

| | Coverable lines | Covered lines | Diff coverage | | ------------- | ------------- | ------------- | ------------- | | Pull request (#1218) | 0 | 0 | **∅ (not applicable)** | **Diff coverage** is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: `/ * 100%`

See your quality gate settings    Change summary preferences

_{Codacy stopped sending the deprecated coverage status on June 5th, 2024. Learn more}

[msimberg]

The GCC14/HIP conflict seems to be the same issue as reported here: https://github.com/llvm/llvm-project/issues/69288. That one is about clang in CUDA mode, but the error looks exactly the same otherwise. I will add some comments in the code and a conflict if GCC 12 seems to be working fine.

[msimberg]

I've added some sort of conflict in upstream spack: https://github.com/spack/spack/pull/46291.