Revert "test: move all test keys/certs under test/fixtures/keys/"

PR-URL: https://github.com/nodejs/node/pull/28083
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Refael Ackermann (רפאל פלחי) <refack@gmail.com>

test/parallel/test-https-unix-socket-self-signed.js

@@ -10,8 +10,8 @@ tmpdir.refresh();
 const fixtures = require('../common/fixtures');
 const https = require('https');
 const options = {
-  cert: fixtures.readKey('rsa_cert.crt'),
-  key: fixtures.readKey('rsa_private.pem')
+  cert: fixtures.readSync('test_cert.pem'),
+  key: fixtures.readSync('test_key.pem')
 };
 
 const server = https.createServer(options, common.mustCall((req, res) => {