Fix DYLD_* propagation to Python process from fish shell (#38615)

share/spack/setup-env.fish

@@ -372,7 +372,14 @@ end
 
 
 function spack_runner -d "Runner function for the `spack` wrapper"
-
+    # Store DYLD_* variables from spack shell function
+    # This is necessary because MacOS System Integrity Protection clears
+    # variables that affect dyld on process start.
+    for var in DYLD_LIBRARY_PATH DYLD_FALLBACK_LIBRARY_PATH
+        if set -q $var
+            set -gx SPACK_$var $$var
+        end
+    end
 
     #
     # Accumulate initial flags for main spack command