[UPDATE] Update environs requirement from <16,>=6.0.5 to >=15.0.1,<16

Updates the requirements on [environs](https://github.com/sloria/environs) to permit the latest version.
- [Changelog](https://github.com/sloria/environs/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sloria/environs/compare/6.1.0...15.0.1)

---
updated-dependencies:
- dependency-name: environs
  dependency-version: 15.0.1
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

pyproject.toml

@@ -45,7 +45,7 @@ dependencies = [
     "pydantic-extra-types>=2.11.1,<3.0.0",
     "ical>=12.0.0,<14.0.0",
     "redis[hiredis]>=3.4.0,<8.0.0",
-    "environs[django]>=6.0.5,<16",
+    "environs[django]>=15.0.1,<16",
     "requests>=2.34.2,<3.0.0",
     "honcho>=2.0.0",
     "psutil>=7.2.2,<8.0.0",