fix(tvix/castore): also set SSL_CERT_FILE for tests there

For everything using reqwest here during test cases, we also need to
set SSL_CERT_FILE.

Change-Id: If8aeda65f3d75cb9ac5c9bc64e37a0cb7dffc17c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11092
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
Tested-by: BuildkiteCI

tvix/castore/default.nix

@@ -2,4 +2,7 @@
 
 depot.tvix.crates.workspaceMembers.tvix-castore.build.override {
   runTests = true;
+  testPreRun = ''
+    export SSL_CERT_FILE=${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt;
+  '';
 }