Fix FileManager directories warning

[jmschonfeld]

Fixes a warning due to lastElement being unconditionally false in the non-FOUNDATION_FRAMEWORK branch

[2025-05-09T17:53:00.386Z] /build/swift-foundation/Sources/FoundationEssentials/FileManager/FileManager+Directories.swift:90:44: warning: will never be executed
[2025-05-09T17:53:00.386Z]  88 |         #endif
[2025-05-09T17:53:00.386Z]  89 |         let urls = Array(_SearchPathURLs(for: directory, in: domain, expandTilde: true))
[2025-05-09T17:53:00.386Z]  90 |         guard let url = lastElement ? urls.last : urls.first else {
[2025-05-09T17:53:00.386Z]     |                         |                  `- warning: will never be executed
[2025-05-09T17:53:00.386Z]     |                         `- note: condition always evaluates to false
[2025-05-09T17:53:00.386Z]  91 |             throw CocoaError(.fileReadUnknown)
[2025-05-09T17:53:00.386Z]  92 |         }

[jmschonfeld]

@swift-ci please test