proj: fix build on Hydra

Tests need access to writable home directory.

Also make the temporary directory (as searched by the tests) writable,
for completeness, although those tests seem to exit early when they
cannot write to the temporary directory without reaching an assert (and
thus without failing).

Fixes #146358

pkgs/development/libraries/proj/default.nix

@@ -42,6 +42,11 @@ stdenv.mkDerivation rec {
     "-DRUN_NETWORK_DEPENDENT_TESTS=OFF"
   ];
 
+  preCheck = ''
+    export HOME=$TMPDIR
+    export TMP=$TMPDIR
+  '';
+
   doCheck = true;
 
   meta = with lib; {