Update pyproject-fmt requirement from <1.3 to <1.6

Updates the requirements on [pyproject-fmt](https://github.com/tox-dev/pyproject-fmt) to permit the latest version.
- [Release notes](https://github.com/tox-dev/pyproject-fmt/releases)
- [Commits](tox-dev/pyproject-fmt@0.1.0...1.5.1)

---
updated-dependencies:
- dependency-name: pyproject-fmt
  dependency-type: direct:production
...

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

pyproject.toml

@@ -63,7 +63,7 @@ develop = [
   "black<24",
   "mypy==1.7.1",
   "poethepoet<1",
-  "pyproject-fmt<1.3",
+  "pyproject-fmt<1.6",
   "ruff==0.1.8",
   "validate-pyproject<0.16",
 ]