Fix typo in Routes course

[Mohamedsayhii]

Fixed a typo in the first paragraph of the Paths section, from /message/all to /messages/all since the course is referring to the paths matching:
"while /messages/all only matches if the path is /messages/all (not /messages, nor /messages/new)"

Because

message/all doesn't match messages/all so we need to change message to messages as it needs to match the next paths in the same paragraph.

This PR

• Changed message/all to messages/all

Issue

Closes #XXXXX

Additional Information

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