🚨(backend) update Ruff config to suppress deprecation warning

When running make ruff-check, a warning informs the user that
some config are deprecated, and gives her the step to migrate.

This warning appears after Ruff released its v0.2.0.
Fix it, by keeping our pyproject.toml up to date.

src/backend/pyproject.toml

@@ -93,7 +93,6 @@ exclude = [
     "__pycache__",
     "*/migrations/*",
 ]
-ignore= ["DJ001", "PLR2004"]
 line-length = 88
 
 
@@ -114,12 +113,13 @@ select = [
     "SLF", # flake8-self
     "T20", # flake8-print
 ]
+ignore= ["DJ001", "PLR2004"]
 
 [tool.ruff.lint.isort]
 section-order = ["future","standard-library","django","third-party","people","first-party","local-folder"]
 sections = { people=["core"], django=["django"] }
 
-[tool.ruff.per-file-ignores]
+[tool.ruff.lint.per-file-ignores]
 "**/tests/*" = ["S", "SLF"]
 
 [tool.pytest.ini_options]