Fix Drupal Coding Standard Errors

Problem/Motivation

$ phpcs --standard=Drupal .

FILE: /do_username/src/Plugin/Validation/Constraint/UsernameFormatConstraint.php
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FOUND 5 ERRORS AFFECTING 5 LINES
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 17 | ERROR | Missing member variable doc comment
 18 | ERROR | Missing member variable doc comment
 19 | ERROR | Missing member variable doc comment
 20 | ERROR | Missing member variable doc comment
 21 | ERROR | Missing member variable doc comment
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FILE: /do_username/src/Plugin/Validation/Constraint/UsernameFormatConstraintValidator.php
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FOUND 9 ERRORS AFFECTING 9 LINES
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 32 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 34 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 36 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 38 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 40 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 42 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 44 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 46 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
 48 | ERROR | [x] Inline comments must end in full-stops, exclamation marks, question marks, colons, or closing parentheses
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FILE: /do_username/tests/src/Kernel/ConfigTest.php
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FOUND 2 ERRORS AFFECTING 2 LINES
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  7 | ERROR | [ ] Missing short description in doc comment
 13 | ERROR | [x] Doc comment short description must end with a full stop
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Proposed resolution

Fix the errors as per Drupal coding standards.

User interface changes

NONE

API changes

NONE

Data model changes

NONE