Support v7 of firebase/php-jwt #156

Currently firebase/php-jwt is pinned to the v6 branch which does not have a secure release.

Version 7 introduces add key size validation with the note:

NOTE: This fix will cause keys with a size below the minimally allowed size to break.

From a scan of the code, this could impact tests as decode is called by the JWT matcher at https://github.com/imbo/behat-api-extension/blob/main/src/ArrayContainsComparator/Matcher/JWT.php#L75

From what I can tell, no code changes are need to support 7 other than consumers of this package potentially having some tests fail if they fail the new key validation.

I have not tested this as I do not have any JWT tests - and have been working around the composer audit failure with composer require --dev firebase/php-jwt:'7.0.5 as 6.11.1'