fix: clean up idle http conns on wsconncache close (#6471)

See https://github.com/coder/coder/actions/runs/4346769070/jobs/7593243836

coderd/wsconncache/wsconncache.go

@@ -121,6 +121,7 @@ func (c *Cache) Acquire(r *http.Request, id uuid.UUID) (*Conn, func(), error) {
 				}
 				c.connMap.Delete(id.String())
 				c.connGroup.Forget(id.String())
+				transport.CloseIdleConnections()
 				_ = conn.Close()
 			}()
 			return conn, nil

coderd/wsconncache/wsconncache_test.go

@@ -126,15 +126,15 @@ func TestCache(t *testing.T) {
 					Host:   fmt.Sprintf("127.0.0.1:%d", tcpAddr.Port),
 					Path:   "/",
 				})
+				ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitMedium)
+				defer cancel()
 				req := httptest.NewRequest(http.MethodGet, "/", nil)
+				req = req.WithContext(ctx)
 				conn, release, err := cache.Acquire(req, uuid.Nil)
 				if !assert.NoError(t, err) {
 					return
 				}
 				defer release()
-
-				ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitMedium)
-				defer cancel()
 				if !conn.AwaitReachable(ctx) {
 					t.Error("agent not reachable")
 					return