Fix FastLapack test to use GenericLUFactorization as always_loaded

Updated the FastLapack test to use GenericLUFactorization as the always_loaded
algorithm instead of FastLUFactorization. This ensures the test can correctly
verify fallback behavior since GenericLUFactorization is always available
while FastLUFactorization requires the FastLapackInterface extension.

When the preference system is fully active:
- best_algorithm = FastLUFactorization (when extension loaded)
- best_always_loaded = GenericLUFactorization (fallback when not loaded)

This provides a realistic test scenario where the always_loaded algorithm
can actually be chosen when the best algorithm is not available.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

test/preferences.jl

@@ -58,9 +58,13 @@ using Preferences
     @testset "FastLapack Extension Conditional Loading" begin
         # Test FastLapack loading conditionally and algorithm availability
 
-        # Preferences should still be set
-        @test Preferences.load_preference(LinearSolve, "best_algorithm_Float64_medium", nothing) == "RFLUFactorization"
-        @test Preferences.load_preference(LinearSolve, "best_always_loaded_Float64_medium", nothing) == "FastLUFactorization"
+        # Set preferences with GenericLU as always_loaded so it can be hit correctly
+        Preferences.set_preferences!(LinearSolve, "best_algorithm_Float64_medium" => "FastLUFactorization"; force = true)
+        Preferences.set_preferences!(LinearSolve, "best_always_loaded_Float64_medium" => "GenericLUFactorization"; force = true)
+        
+        # Verify preferences are set
+        @test Preferences.load_preference(LinearSolve, "best_algorithm_Float64_medium", nothing) == "FastLUFactorization"
+        @test Preferences.load_preference(LinearSolve, "best_always_loaded_Float64_medium", nothing) == "GenericLUFactorization"
 
         A = rand(Float64, 150, 150) + I(150)
         b = rand(Float64, 150)