Fix race condition in httprs test

The `So(server, ShouldNotBeNil)` call in the httprs test attempts to
print a string representation of the `server`, but this is racy because
the reconnection state is initialized in a
Goroutine. `httptest.NewServer()` always returns a valid value, so we
can drop this test.

Relates to https://gitlab.com/gitlab-org/gitlab-workhorse/-/issues/285

changelogs/unreleased/sh-fix-httprs-race-condition.yml

+---
+title: Fix race condition in httprs test
+merge_request: 584
+author:
+type: fixed

internal/httprs/httprs_test.go

@@ -111,7 +111,6 @@ func TestHttpWebServer(t *testing.T) {
 		So(err, ShouldBeNil)
 
 		server := httptest.NewServer(http.FileServer(http.Dir(dir)))
-		So(server, ShouldNotBeNil)
 
 		Convey("When requesting /file", func() {
 			res, err := http.Get(server.URL + "/file")