chore: bump php-cs-fixer to 3.54.0

[phil-davis]

Note php-cs-fixer now complains about 'binary_operator_spaces' being set to an empty array.
It wants the default setting to be explicitly mentioned.

$ composer cs-fixer
> php-cs-fixer fix
PHP CS Fixer 3.54.0 15 Keys Accelerate by Fabien Potencier, Dariusz Ruminski and contributors.
PHP runtime: 7.4.3-4ubuntu2.20
Loaded config default from "/home/phil/git/sabre-io/Baikal/.php-cs-fixer.dist.php".
Using cache file ".php-cs-fixer.cache".
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In FixerFactory.php line 164:
                                                                                 
  [binary_operator_spaces] Configuration must be an array and may not be empty.  
                                                                                 

fix [--path-mode PATH-MODE] [--allow-risky ALLOW-RISKY] [--config CONFIG] [--dry-run] [--rules RULES] [--using-cache USING-CACHE] [--cache-file CACHE-FILE] [--diff] [--format FORMAT] [--stop-on-violation] [--show-progress SHOW-PROGRESS] [--] [<path>...]

Script php-cs-fixer fix handling the cs-fixer event returned with error code 32

So I have chosen 'at_least_single_space' - that allows existing to pass cs-fixer.

The various settings options are mentioned here:
https://cs.symfony.com/doc/rules/operator/binary_operator_spaces.html

[phil-davis]

See dependabot PR #1262