test: fix flaky test-http2-session-timeout

Increase server timeout, reduce frequency of calls and
unbind timeout after runs are done in order to avoid
race conditions. Temporarily moved to sequential.

Fixes: #15326

test/parallel/test-http2-session-timeout.js → test/sequential/test-http2-session-timeout.js

@@ -7,20 +7,22 @@ if (!common.hasCrypto)
 const h2 = require('http2');
 
 const serverTimeout = common.platformTimeout(200);
-const callTimeout = common.platformTimeout(10);
+const callTimeout = common.platformTimeout(20);
+const minRuns = Math.ceil(serverTimeout / callTimeout) * 2;
+const mustNotCall = common.mustNotCall();
 
 const server = h2.createServer();
 server.timeout = serverTimeout;
 
 server.on('request', (req, res) => res.end());
-server.on('timeout', common.mustNotCall());
+server.on('timeout', mustNotCall);
 
 server.listen(0, common.mustCall(() => {
   const port = server.address().port;
 
   const url = `http://localhost:${port}`;
   const client = h2.connect(url);
-  makeReq(40);
+  makeReq(minRuns);
 
   function makeReq(attempts) {
     const request = client.request({
@@ -29,13 +31,17 @@ server.listen(0, common.mustCall(() => {
       ':scheme': 'http',
       ':authority': `localhost:${port}`,
     });
+    request.resume();
     request.end();
 
-    if (attempts) {
-      setTimeout(() => makeReq(attempts - 1), callTimeout);
-    } else {
-      server.close();
-      client.destroy();
-    }
+    request.on('end', () => {
+      if (attempts) {
+        setTimeout(() => makeReq(attempts - 1), callTimeout);
+      } else {
+        server.removeListener('timeout', mustNotCall);
+        client.destroy();
+        server.close();
+      }
+    });
   }
 }));