[BUGFIX] Show exception in linkvalidator report

For \GuzzleHttp\Exception\RequestException the exception message
is now shown as well (as for the other exceptions). This makes
it easier to interpret the error messages as this exception may
be thrown for a number of reasons, such as not existing domain,
problem with SSL certificate etc.

Resolves: #89376
Releases: master, 9.5
Change-Id: If5cd24e35afdbdede37379fab4055eff84933f48
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61909


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Jörg Bösche <typo3@joergboesche.de>
Tested-by: Julian Geils <j_geils@web.de>
Tested-by: Sascha Rademacher <sascha.rademacher+typo3@gmail.com>
Tested-by: Steffen Frese <steffenf14@gmail.com>
Tested-by: Henning Liebe <h.liebe@neusta.de>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Jörg Bösche <typo3@joergboesche.de>
Reviewed-by: Julian Geils <j_geils@web.de>
Reviewed-by: Sascha Rademacher <sascha.rademacher+typo3@gmail.com>
Reviewed-by: Felix P. <f.pachowsky@neusta.de>
Reviewed-by: Steffen Frese <steffenf14@gmail.com>
Reviewed-by: Henning Liebe <h.liebe@neusta.de>
Reviewed-by: Susanne Moog <look@susi.dev>