Update simplesamlphp/assert requirement (#364)

Updates the requirements on [simplesamlphp/assert](https://github.com/simplesamlphp/assert) to permit the latest version.

Updates `simplesamlphp/assert` to 1.4.0
- [Commits](simplesamlphp/assert@v1.3.1...v1.4.0)

---
updated-dependencies:
- dependency-name: simplesamlphp/assert
  dependency-type: direct:production
  dependency-group: production-dependencies
...

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composer.json

@@ -31,7 +31,7 @@
         "psr/clock": "^1.0",
         "psr/http-message": "^2.0",
         "psr/log": "^2.0 || ^3.0",
-        "simplesamlphp/assert": "~1.3.1",
+        "simplesamlphp/assert": "~1.4.0",
         "simplesamlphp/xml-common": "~1.18.0",
         "simplesamlphp/xml-security": "~1.9.5",
         "simplesamlphp/xml-soap": "~1.5.3"