Merge bitcoin/bitcoin#29881: guix: use GCC 13 to build releases

0c1b29a057 ci: use GCC 13 for some jobs (fanquake)
cbc65b3ad5 guix: use GCC 13.3.0 for base toolchain. (fanquake)

Pull request description:

  Switch release builds to using GCC 13.3.0: https://gcc.gnu.org/gcc-13/, which landed in Guix in: https://git.savannah.gnu.org/cgit/guix.git/commit/?id=750148ce1ea6c65a7c14424546db0078161f7e17.

  Does not solve the cross-arch non-determinism for `powerpc64le-linux-gnu` builds.

ACKs for top commit:
  achow101:
    ACK 0c1b29a057
  hebasto:
    ACK 0c1b29a057.
  TheCharlatan:
    Re-ACK 0c1b29a057

Tree-SHA512: eb3f091278d371166eb1df4718b6d0d68b09db65291d563dddd581964f2b488f901e4ba43831a699e2d0fd053d6e9038a307cbea78d5597da77699c34b440ea6

contrib/guix/manifest.scm

@@ -90,7 +90,7 @@ chain for " target " development."))
       (home-page (package-home-page xgcc))
       (license (package-license xgcc)))))
 
-(define base-gcc gcc-12) ;; 12.4.0
+(define base-gcc gcc-13) ;; 13.3.0
 
 (define base-linux-kernel-headers linux-libre-headers-6.1)
 
@@ -542,7 +542,7 @@ inspecting signatures in Mach-O binaries.")
         gzip
         xz
         ;; Build tools
-        gcc-toolchain-12
+        gcc-toolchain-13
         cmake-minimal
         gnu-make
         ;; Scripting
@@ -561,7 +561,7 @@ inspecting signatures in Mach-O binaries.")
           ((string-contains target "-linux-")
            (list bison
                  pkg-config
-                 (list gcc-toolchain-12 "static")
+                 (list gcc-toolchain-13 "static")
                  (make-bitcoin-cross-toolchain target)))
           ((string-contains target "darwin")
            (list clang-toolchain-18