Update repositories.txt

[christosneg]

added concurrentPID library

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/christosneg/concurrentPID.git:

Linting library in concurrentPID
WARNING: A commonly misspelled word was found in the library.properties paragraph field. Suggested correction: This     
         library contains 2 classes PID and ConcurrentPID. The PID class is a blueprint for a basic PID controller that 
         must be inherited and ConcurrentPID class can control many PID objects concurrently.                           
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format         
         (Rule LP035)                                                                                                   
WARNING: library.properties includes field item(s) Arduino.h not found in library.                             
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format
         (Rule LP052)                                                                                          
WARNING: No example sketches found. Please provide examples.                                      
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#library-examples
         (Rule LD004)                                                                             
WARNING: Potentially misspelled examples folder name found: concurrentPID/example                 
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#library-examples
         (Rule LD005)                                                                             

Linter results for project: 0 ERRORS, 4 WARNINGS

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[github-actions]

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