[7.x] Ignore SlevomatCodingStandard sniffs in codesniffer 3.7.1+

Due to the newer versions of coder (8.3.16) and codesniffer (3.7.1) we have four coding standards messages to fix for 7.x-1.x

FILE: scheduler/scheduler.edit.inc
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FOUND 2 ERRORS AFFECTING 2 LINES
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 46 | ERROR | [x] Use null coalesce operator instead of ternary operator.
    |       |     (SlevomatCodingStandard.ControlStructures.RequireNullCoalesceOperator.NullCoalesceOperatorNotUsed)
 47 | ERROR | [x] Use null coalesce operator instead of ternary operator.
    |       |     (SlevomatCodingStandard.ControlStructures.RequireNullCoalesceOperator.NullCoalesceOperatorNotUsed)
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PHPCBF CAN FIX THE 2 MARKED SNIFF VIOLATIONS AUTOMATICALLY
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FILE: scheduler/tests/scheduler.test
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FOUND 2 ERRORS AFFECTING 2 LINES
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  575 | ERROR | [x] list(...) is forbidden, use [...] instead.
      |       |     (SlevomatCodingStandard.PHP.ShortList.LongListUsed)
 1592 | ERROR | [x] list(...) is forbidden, use [...] instead.
      |       |     (SlevomatCodingStandard.PHP.ShortList.LongListUsed)
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PHPCBF CAN FIX THE 2 MARKED SNIFF VIOLATIONS AUTOMATICALLY
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