fix flake8 warnings

conanfile.py

@@ -27,6 +27,7 @@ from conan import ConanFile
 from conan.tools.cmake import CMake, CMakeDeps, CMakeToolchain
 from conan.tools.files import copy, load, rmdir
 from conan.tools.scm import Version
+from conans.errors import ConanInvalidConfiguration
 from conans.tools import (  # TODO replace with new tools for Conan 2.0
     check_min_cppstd,
     get_env,

docs/conf.py

@@ -9,9 +9,10 @@
     :license: BSD, see LICENSE for details.
 """
 
+import os
 import re
+import subprocess
 
-import sphinx_rtd_theme
 from pygments.lexer import (
     RegexLexer,
     bygroups,
@@ -482,10 +483,6 @@ lexers["cpp"] = MyCppLexer(startinline=True)
 # For a full list see the documentation:
 # https://www.sphinx-doc.org/en/master/usage/configuration.html
 
-import os
-import re
-import subprocess
-
 
 def get_version():
     try: