minor #37121 [Contracts] Add missing "extra.thanks" entries in composer.json (nicolas-grekas)

This PR was merged into the 5.2-dev branch.

Discussion
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[Contracts] Add missing "extra.thanks" entries in composer.json

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Something we forgot and that might help give some more visibility to symfony/contracts.

Commits
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bd04f0cce6 [Contracts] Add missing "extra.thanks" entries in composer.json

Author: nicolas-grekas

composer.json

@@ -29,6 +29,10 @@
     "extra": {
         "branch-alias": {
             "dev-master": "1.1-dev"
+        },
+        "thanks": {
+            "name": "symfony/contracts",
+            "url": "https://github.com/symfony/contracts"
         }
     }
 }