fix(ci): install poetry before build (#10)

pyproject.toml

@@ -29,7 +29,7 @@ build-backend = "poetry.core.masonry.api"
 version_toml = [
     "pyproject.toml:tool.poetry.version",
 ]
-build_command = "poetry build"
+build_command = "pip install poetry && poetry build"
 commit_message = "{version}\n\nAutomatically generated by python-semantic-release"
 commit_parser = "angular"
 logging_use_named_masks = false