Avoid deprecation warnings on PHP 8.4

[eiriksm]

These are the warnings I am getting, which I am hoping to fix with this PR

Deprecated: Bitbucket\Client::__construct(): Implicitly marking parameter $httpClientBuilder as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/Client.php on line 102

Deprecated: Bitbucket\Client::authenticate(): Implicitly marking parameter $password as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/Client.php on line 210

Deprecated: Bitbucket\HttpClient\Builder::__construct(): Implicitly marking parameter $httpClient as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/HttpClient/Builder.php on line 92

Deprecated: Bitbucket\HttpClient\Builder::__construct(): Implicitly marking parameter $requestFactory as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/HttpClient/Builder.php on line 92

Deprecated: Bitbucket\HttpClient\Builder::__construct(): Implicitly marking parameter $streamFactory as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/HttpClient/Builder.php on line 92

Deprecated: Bitbucket\HttpClient\Plugin\Authentication::__construct(): Implicitly marking parameter $password as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/HttpClient/Plugin/Authentication.php on line 49

Deprecated: Bitbucket\HttpClient\Plugin\Authentication::buildAuthorizationHeader(): Implicitly marking parameter $password as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/HttpClient/Plugin/Authentication.php on line 81

Deprecated: Bitbucket\ResultPager::__construct(): Implicitly marking parameter $perPage as nullable is deprecated, the explicit nullable type must be used instead in phar:///app/runner/vendor/bitbucket/client/src/ResultPager.php on line 68