Revert "python3Packages.google-cloud-iam: 2.19.0 -> 3.31.3"

This reverts commit 984c12a990 due to a
bad update.

pkgs/development/python-modules/google-cloud-iam/default.nix

@@ -17,14 +17,14 @@
 
 buildPythonPackage rec {
   pname = "google-cloud-iam";
-  version = "3.31.3";
+  version = "2.19.0";
   pyproject = true;
 
   src = fetchFromGitHub {
     owner = "googleapis";
     repo = "google-cloud-python";
-    tag = "google-cloud-build-v${version}";
-    hash = "sha256-qQ+8X6I8lt4OTgbvODsbdab2dYUk0wxWsbaVT2T651U=";
+    tag = "google-cloud-iam-v${version}";
+    hash = "sha256-E1LISOLQcXqUMTTPLR+lwkR6gF1fuGGB44j38cIK/Z4=";
   };
 
   sourceRoot = "${src.name}/packages/google-cloud-iam";