guix: use clang-toolchain-17 for macOS build

Version is 17.0.6.

contrib/guix/manifest.scm

@@ -525,5 +525,5 @@ inspecting signatures in Mach-O binaries.")
           ((string-contains target "-linux-")
            (list (make-bitcoin-cross-toolchain target)))
           ((string-contains target "darwin")
-           (list clang-toolchain-15 binutils cmake-minimal python-signapple zip))
+           (list clang-toolchain-17 binutils cmake-minimal python-signapple zip))
           (else '())))))