chore: bump black from 24.10 to 26.3.1

Fixes high severity CVE in black's cache file handling.
black is a dev-only dependency; end users are not affected.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jacalata

pyproject.toml

@@ -33,7 +33,7 @@ classifiers = [
 repository = "https://github.com/tableau/server-client-python"
 
 [project.optional-dependencies]
-test = ["black==24.10", "build", "mypy==1.4", "pytest>=7.0", "pytest-cov", "pytest-subtests",
+test = ["black==26.3.1", "build", "mypy==1.4", "pytest>=7.0", "pytest-cov", "pytest-subtests",
     "pytest-xdist", "requests-mock>=1.0,<2.0", "types-requests>=2.32.4.20250913"]
 
 [tool.setuptools.package-data]