withMockedHome: Don't swallow errors

The code was silently swallowing errors coming from the function under
test, so errors in the tests did not surface as test failures.
This throws the error if the cleaning the bin directory doesn't fail
first.

Author: etcwilde

Tests/SwiftlyTests/SwiftlyTests.swift

@@ -336,6 +336,7 @@ public enum SwiftlyTests {
                 if cleanBinDir {
                     try await fs.remove(atPath: Swiftly.currentPlatform.swiftlyBinDir(Self.ctx))
                 }
+                throw error
             }
         }
     }