Pin cabal-experimental to pre-regression version (#227)
The cabal-experimental update from 7e50837 (Apr 2025) to bc52b09 (Aug 2025) introduced a change in pkgsUseSharedLibrary (commit f47840db) that stopped checking the compiler's capabilities when deciding whether to build shared libraries. This causes store dependencies (e.g. os-string) to be installed without .dyn_hi files, while project packages (e.g. tar) are still built with -dynamic-too, resulting in missing dynamic interface file errors. Pin back to the known-working version until the regression is resolved upstream.