style(tests): wrap long subprocess -c argument under line-length=100

The hardened fallback test in commit 78afc07 introduced a line
that was 101 chars (one over ruff's configured line-length=100).
Splits the literal into two adjacent string literals via implicit
concatenation; semantics unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ayhammouda

tests/test_packaging.py

@@ -159,7 +159,10 @@ def test_source_tree_import_without_installed_metadata(self, tmp_path: Path):
                 sys.executable,
                 "-S",
                 "-c",
-                prelude + "import mcp_server_python_docs; print(mcp_server_python_docs.__version__)",
+                prelude + (
+                    "import mcp_server_python_docs; "
+                    "print(mcp_server_python_docs.__version__)"
+                ),
             ],
             capture_output=True,
             text=True,