Revert Merge #228209: gtest: 1.12.1 -> 1.13.0

This reverts commit 3c75a19be62086753705876cc93f2c280af68a04, reversing
changes made to cfd87655c8c9d6dfef423f3a1be51a3ad92a3368.

Doesn't seem suitable for nixpkgs 23.05 anymore, etc. See
https://github.com/NixOS/nixpkgs/pull/228209#issuecomment-1536888736

pkgs/development/libraries/gtest/default.nix

···
 
 stdenv.mkDerivation rec {
   pname = "gtest";
-  version = "1.13.0";
+  version = "1.12.1";
 
   outputs = [ "out" "dev" ];
 
   src = fetchFromGitHub {
     owner = "google";
     repo = "googletest";
-    rev = "v${version}";
-    hash = "sha256-LVLEn+e7c8013pwiLzJiiIObyrlbBHYaioO/SWbItPQ=";
+    rev = "release-${version}";
+    hash = "sha256-W+OxRTVtemt2esw4P7IyGWXOonUN5ZuscjvzqkYvZbM=";
   };
 
   patches = [