"tlmgr install" would warn about "check_file_and_remove: neither
checksum nor checksize available for ..." and may exit with an error,
although the package is correctly installed.  So ignore the error exit.

It seems the latest tlmgr fixed the error exit; i.e., it still prints
the warning but doesn't exit with an error.

Credit: https://tug.org/pipermail/tex-live/2022-November/048688.html

Already installed in the runner image.

See: https://github.com/actions/runner-images/blob/main/images/ubuntu/Ubuntu2204-Readme.md

The 'ubuntu-latest' image was Ubuntu 22.04 but has been Ubuntu 24.04,
and this caused the 'fontawesome5.tar.xz' package failing to install:

```
TeXLive::TLUtils::check_file_and_remove: neither checksum nor checksize available for /tmp/sZbRLtVCfX/7Rk9CYBNzM/fontawesome5.tar.xz, cannot check integrityUndefined subroutine &TeXLive::TLPDB::_post_install_package called at /usr/share/texlive/tlpkg/TeXLive/TLPDB.pm line 1665, <TMP> line 54.
```

Fix it by changing 'ubuntu-latest' to 'ubuntu-22.04'.

Issue: #23

- No need to install the 'texlive-plain-generic' package after removing
  the 'ulem' package.
- Use 'apt-get' instead of 'apt' because the former is more suitable for
  non-interactive usage.
- Ignore certificate check in wget to avoid possible outdated root CA
  bundle.