Potential caching bug when changing solve-group

[uwu-420]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

• Create a fresh project with this pyproject.toml.

[project]
name = "pixi-test"
requires-python = ">=3.13"
version = "0.1.0"
dependencies = []

[tool.pixi.project]
channels = ["conda-forge"]
platforms = ["osx-64", "osx-arm64"]

[tool.pixi.feature.foo]
platforms = ["osx-64"]

[tool.pixi.feature.foo.dependencies]
fastapi = ">=0.115"

[tool.pixi.feature.bar]
platforms = ["osx-arm64"]

[tool.pixi.feature.bar.dependencies]
fastapi = "<0.115"

[tool.pixi.environments]
foo = {features = ["foo"], solve-group = "default"}
bar = {features = ["bar"], solve-group = "default"}

• Run pixi install which will fail as expected due to the conflicting dependency in the default solve-group.
• Change the solve-group of the bar environment to something other than "default" (I just chose "other").
• Run pixi install again and it should successfully resolve everything as expected.
• Change back the solve-group of the bar environment to "default"
• Run pixi install again. It does not fail although it should due to the dependency conflicts in the "default" solve-group.

Issue description

I think the example above shows that there are some caching issues which cause pixi to be fine with dependency conflicts that are usually caught by the solver.

Expected behavior

The last pixi install should have shown the same error as the very first pixi install