protonmail-bridge-gui: fix whitespace in cmakeFlags

Use __structuredAttrs after 53f550b

pkgs/by-name/pr/protonmail-bridge-gui/package.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation (finalAttrs: {
   patches = [
     # Use `gtest` from Nixpkgs to allow an offline build
     ./use-nix-googletest.patch
-    # From https://github.com/ProtonMail/proton-bridge/pull/502 hopefully superceded by next upstream release
+    # From https://github.com/ProtonMail/proton-bridge/pull/502 and expected to be included in next upstream release
     ./0001-Fix-ColorImage-Qt-crash.patch
     ./0002-Avoid-name-clash-with-6.8-introduced-popupType.patch
   ];
@@ -65,6 +65,8 @@ stdenv.mkDerivation (finalAttrs: {
     sed -i "/add_subdirectory(bridge-gui-tester)/d" CMakeLists.txt
   '';
 
+  __structuredAttrs = true; # to allow spaces in `cmakeFlags`
+
   cmakeFlags = [
     "-DBRIDGE_APP_FULL_NAME=Proton Mail Bridge"
     "-DBRIDGE_VENDOR=Proton AG"