test: make test-dh-regr more efficient where possible

test-dh-regr is timing out in CI because crypto.createDiffieHellman() is
considerably slower after an OpenSSL upgrade. This PR modifies the
change from 11ad744 which made the test
FIPS-compatible. When not in FIPS mode, the test will use a shorter key
which will enable it to run much faster.

PR-URL: #28390
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

Author: Trott

test/pummel/test-dh-regr.js

@@ -27,7 +27,11 @@ if (!common.hasCrypto)
 const assert = require('assert');
 const crypto = require('crypto');
 
-const p = crypto.createDiffieHellman(1024).getPrime();
+// FIPS requires length >= 1024 but we use 256 in this test to keep it from
+// taking too long and timing out in CI.
+const length = common.hasFipsCrypto ? 1024 : 256;
+
+const p = crypto.createDiffieHellman(length).getPrime();
 
 for (let i = 0; i < 2000; i++) {
   const a = crypto.createDiffieHellman(p);