patchShebangs: fix crash on read-only files

Fixes a regression introduced by c1cc6ff0c0680ae6d8228953ebba93c131e04775 where patchShebangs would crash if a file is read-only

pkgs/build-support/setup-hooks/patch-shebangs.sh

@@ -72,12 +72,25 @@ patchShebangs() {
     _sponge() {
         local content
         local target
+        local restoreReadOnly
         content=""
         target="$1"
+
+        # Make file writable if it is read-only
+        if [[ ! -w "$target" ]]; then
+            chmod +w "$target"
+            restoreReadOnly=true
+        fi
+
         while IFS= read -r line || [[ -n "$line" ]]; do
             content+="$line"$'\n'
         done
         printf '%s' "$content" > "$target"
+
+        # Restore read-only if it was read-only before
+        if [[ -n "${restoreReadOnly:-}" ]]; then
+            chmod -w "$target"
+        fi
     }
 
     local f