fix: update Config.read() signature (overrides, tags)

[kimbyungnam]

Purpose

This PR fixes an incompatibility with newer Sphinx versions (≥ 9) when using sphinx-multiversion on Python 3.11+.

Starting from Sphinx 8.2.0, Python 3.11+ is required.
sphinx-multiversion officially supports Python 8–12, but it currently does not restrict the Sphinx version
As a result, when users run sphinx-multiversion on Python 3.11 or newer, Sphinx 9+ is automatically installed

In Sphinx 9, the signature of Config.read() requires keyword arguments:
However, sphinx-multiversion was still calling it using the old positional-style API, causing runtime errors when used with Sphinx ≥ 9 (see #201).

Resolves #201

Solution Sketch

This PR updates all calls to Config.read() to:

• Pass arguments explicitly as keyword arguments
• Provide a Tags() instance explicitly

The parameter names (overrides, tags) are consistent across Sphinx 7 through 9, so using keyword arguments is safe and compatible across Python 3.8–3.12

• Avoids introducing conditional logic based on Sphinx versions
• Maintains backward compatibility with older supported Sphinx releases
• Fixes the issue without tightening dependency constraints
• Aligns with the current Sphinx public API

[bmos]

@Holzhaus