Pin to Ubuntu 22.04 to fix Puppeteer (#940)

From Puppeteer docs:

> Ubuntu 23.10+ (or possibly other Linux distros in the future) ship an
AppArmor profile that applies to Chrome stable binaries installed at
/opt/google/chrome/chrome (the default installation path). This policy
is stored at /etc/apparmor.d/chrome. This AppArmor policy prevents
Chrome for Testing binaries downloaded by Puppeteer from using user
namespaces resulting in the `No usable sandbox!` error when trying to
launch the browser

We are currently seeing this error in CI due to our usage of
`ubuntu-latest` in our CI Github Action images. It seems that Puppeteer
has disabled this check as part of
puppeteer/puppeteer#13196, but it doesn't look
like this has been released yet. Once it has, we could potentially
update to that latest version of Puppeteer and reinstate usage of
`ubuntu-latest`. In the meantime, though, this pins our CI image to
`ubuntu-22.04` to get CI to pass.

---------

Signed-off-by: Steve Ayers <[email protected]>

Author: smaye81

.github/workflows/ci.yaml

@@ -9,7 +9,10 @@ permissions:
   contents: read
 jobs:
   ci:
-    runs-on: ubuntu-latest
+    # TODO(sayers) - Need to run on 22.04 for the time being until 
+    # https://github.com/puppeteer/puppeteer/pull/13196 is released
+    # See https://github.com/connectrpc/conformance/pull/940 for context
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         # When changing this, don't forget to also update