Switch one fixture to using the [project] table

So we have coverage of both the old and new style dependency
table syntax.

Author: edmorley

spec/fixtures/poetry_basic/poetry.lock

@@ -1,10 +1,16 @@
+[project]
+name = "poetry-basic"
+version = "0.0.0"
+requires-python = ">=3.13"
+dependencies = [
+    "typing-extensions"
+]
+
 [tool.poetry]
 package-mode = false
 
-[tool.poetry.dependencies]
-python = "^3.13"
-typing-extensions = "*"
-
 # This group shouldn't be installed due to us passing `--only main`.
+# Note: We can't use `[dependency-groups]`, since Poetry doesn't yet support PEP735:
+# https://github.com/python-poetry/poetry/issues/9751
 [tool.poetry.group.test.dependencies]
 pytest = "*"

spec/fixtures/poetry_basic/pyproject.toml

@@ -1,6 +1,12 @@
 [tool.poetry]
 package-mode = false
 
+# This test uses the legacy `[tool.poetry]` table instead of `[project.dependencies]`
+# to ensure that our chosen Poetry version still supports apps using the old table.
 [tool.poetry.dependencies]
 python = "^3.9"
 typing-extensions = "*"
+
+# This group shouldn't be installed due to us passing `--only main`.
+[tool.poetry.group.test.dependencies]
+pytest = "*"