Mittwald PHP 7.3 FPM outdated ICU version workaround

Downgrade guzzle to version 6.5.4 with TYPO3 9.5.20 to support an outdated ICU version on the used webspace.txt

[BUGFIX] for Mittwald to support PHP 7.3 FPM
to prevent errors like >IDNA_CHECK_BIDI...<
the guzzle version is fixed to 6.5.4 instead
of version 6.5.5 with the command
composer req guzzlehttp/guzzle:6.5.4 --update-with-all-dependencies

Changelogs summary:

 - symfony/polyfill-intl-normalizer removed (installed version was v1.18.0)

 - symfony/polyfill-intl-idn downgraded from v1.18.0 to v1.17.0
   See changes: https://github.com/symfony/polyfill-intl-idn/compare/v1.18.0...v1.17.0
   Release notes: https://github.com/symfony/polyfill-intl-idn/releases/tag/v1.17.0

 - guzzlehttp/guzzle downgraded from 6.5.5 to 6.5.4
   See changes: https://github.com/guzzle/guzzle/compare/6.5.5...6.5.4
   Release notes: https://github.com/guzzle/guzzle/releases/tag/6.5.4

 - symfony/polyfill-php70 updated from v1.12.0 to v1.18.0
   See changes: https://github.com/symfony/polyfill-php70/compare/v1.12.0...v1.18.0
   Release notes: https://github.com/symfony/polyfill-php70/releases/tag/v1.18.0Changelogs summary:

 - symfony/polyfill-intl-normalizer removed (installed version was v1.18.0)

 - symfony/polyfill-intl-idn downgraded from v1.18.0 to v1.17.0
   See changes: https://github.com/symfony/polyfill-intl-idn/compare/v1.18.0...v1.17.0
   Release notes: https://github.com/symfony/polyfill-intl-idn/releases/tag/v1.17.0

 - guzzlehttp/guzzle downgraded from 6.5.5 to 6.5.4
   See changes: https://github.com/guzzle/guzzle/compare/6.5.5...6.5.4
   Release notes: https://github.com/guzzle/guzzle/releases/tag/6.5.4

 - symfony/polyfill-php70 updated from v1.12.0 to v1.18.0
   See changes: https://github.com/symfony/polyfill-php70/compare/v1.12.0...v1.18.0
   Release notes: https://github.com/symfony/polyfill-php70/releases/tag/v1.18.0