Remove deprecated function db_select(): call

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Line src/Plugin/Block/SliderBlock.php
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28 Call to deprecated function db_select():
in drupal:8.0.0 and is removed from drupal:9.0.0. Instead, get
a database connection injected into your service from the container and
call select() on it. For example,
41 Call to deprecated function db_select():
in drupal:8.0.0 and is removed from drupal:9.0.0. Instead, get
a database connection injected into your service from the container and
call select() on it. For example,