Fix SignedExchangeRequestHandlerRealCertVerifierBrowserTest.Basic

This test has been disabled due to expiration of the test certificate.
It runs against the real (not mocked) cert verifier, which doesn't have
a mechanism to inject a timestamp for verification.

This fixes the test by regenerating the test certificate, which is now
valid until 2024-03-18.

We will track this in crbug.com/1279652, so that next time we can take
action before it expires.

(cherry picked from commit d43e4a541a1e1c7aa22652465cf8415e80b6de2f)

Bug: 1279496,1279652
Change-Id: I53a75122876dee44ce33495aa060aa87dc1eeb56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3337158
Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#951369}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3338530
Commit-Queue: Ben Mason <benmason@chromium.org>
Reviewed-by: Krishna Govind <govind@chromium.org>
Commit-Queue: Krishna Govind <govind@chromium.org>
Owners-Override: Krishna Govind <govind@chromium.org>
Cr-Commit-Position: refs/branch-heads/4664@{#1310}
Cr-Branched-From: 24dc4ee75e01a29d390d43c9c264372a169273a7-refs/heads/main@{#929512}

• content/browser/web_package/signed_exchange_request_handler_browsertest.cc[diff]
• content/test/data/sxg/generate-test-certs.sh[diff]
• content/test/data/sxg/prime256v1-sha256-long-validity.public.pem[diff]
• content/test/data/sxg/test.example.org-long-validity.public.pem.cbor[diff]
• content/test/data/sxg/test.example.org_long_cert_validity.sxg[diff]