Update repositories.txt

[JensDMadsen]

Add Multitasker library to Arduino Library Manager.

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/JensDMadsen/Multitasker:

Linting library in Multitasker
WARNING: Unable to load the library.properties url field: 555                                                  
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format
         (Rule LP042)                                                                                          

Linter results for project: 0 ERRORS, 1 WARNINGS

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Linting sketch in Multitasker/examples/DemoTask1

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/DemoTask2

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/DemoTask3

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/DemoTask4

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/DemoTask5A

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/DemoTask5B

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/DemoTask5C

Linter results for project: no errors or warnings

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Linting sketch in Multitasker/examples/SimpleTask

Linter results for project: no errors or warnings

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Linter results for projects: 0 ERRORS, 1 WARNINGS

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/JensDMadsen/Multitasker/