docs(conf) Fix UP031 (printf-string-formatting)

https://docs.astral.sh/ruff/rules/printf-string-formatting/

docs/conf.py:201:16: UP031 Use format specifiers instead of percent format
    |
195 |         lineno = None
196 |
197 |     linespec = "#L%d-L%d" % (lineno, lineno + len(source) - 1) if lineno else ""
    |                ^^^^^^^^^^ UP031
198 |
199 |     fn = relpath(fn, start=pathlib.Path(vcspull.__file__).parent)
    |
    = help: Replace with format specifiers

docs/conf.py

@@ -198,7 +198,7 @@ def linkcode_resolve(domain: str, info: dict[str, str]) -> t.Union[None, str]:
     except Exception:
         lineno = None
 
-    linespec = "#L%d-L%d" % (lineno, lineno + len(source) - 1) if lineno else ""
+    linespec = f"#L{lineno}-L{lineno + len(source) - 1}" if lineno else ""
 
     fn = relpath(fn, start=pathlib.Path(libvcs.__file__).parent)