test: move some gc tests back to parallel/, unmark flaky

These should no longer be flaky after the libuv update.

Refs: https://github.com/nodejs/node/pull/23336

PR-URL: https://github.com/nodejs/node/pull/23356
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/sequential/sequential.status

@@ -5,19 +5,8 @@ prefix sequential
 # sample-test                       : PASS,FLAKY
 
 [true] # This section applies to all platforms
-# This test will be flaky until https://github.com/libuv/libuv/pull/1742 lands
-# on Node.js.
-test-fs-readfile-tostring-fail: PASS, FLAKY
-# https://github.com/nodejs/node/issues/23066
-test-gc-http-client-timeout: PASS, FLAKY
 # https://github.com/nodejs/node/issues/22336
 test-gc-http-client: PASS,FLAKY
-# https://github.com/nodejs/node/issues/23067
-test-gc-net-timeout: PASS,FLAKY
-# https://github.com/nodejs/node/issues/23089
-test-gc-http-client-onerror: PASS,FLAKY
-# https://github.com/nodejs/node/issues/23219
-test-gc-http-client-connaborted: PASS,FLAKY
 
 [$system==win32]
 # https://github.com/nodejs/node/issues/22327