http2: release request()'s "connect" event listener after it runs

lib/internal/http2/core.js

@@ -1426,7 +1426,7 @@ class ClientHttp2Session extends Http2Session {
 
     const onConnect = requestOnConnect.bind(stream, headersList, options);
     if (this.connecting) {
-      this.on('connect', onConnect);
+      this.once('connect', onConnect);
     } else {
       onConnect();
     }

test/parallel/test-http2-request-remove-connect-listener.js

@@ -0,0 +1,28 @@
+'use strict';
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+const assert = require('assert');
+const http2 = require('http2');
+
+
+const server = http2.createServer();
+server.on('stream', common.mustCall((stream) => {
+  stream.respond();
+  stream.end();
+}));
+
+server.listen(0, common.mustCall(() => {
+  const client = http2.connect(`http://localhost:${server.address().port}`);
+  const req = client.request();
+  client.once('connect', common.mustCall());
+
+  req.on('response', common.mustCall(() => {
+    assert.strictEqual(client.listenerCount('connect'), 0);
+  }));
+  req.on('close', common.mustCall(() => {
+    server.close();
+    client.close();
+  }));
+}));