BUG: fix variable case

Author: bsipocz

tox.ini

@@ -37,7 +37,7 @@ commands =
     # too due to issues with e.g. multiprocessing and problems in upstream dependency
     !buildhtml: bash -c 'if python -c "import platform; print(platform.platform())" | grep -i macos; then cat ignore_osx_testing >> ignore_testing; fi'
     !buildhtml: bash -c 'if python -c "import platform; print(platform.platform())" | grep -i win; then cat ignore_windows_testing >> ignore_testing; fi'
-    !buildhtml: bash -c 'if [[ $CI == True ]]; then cat ignore_gha_testing >> ignore_testing; fi'
+    !buildhtml: bash -c 'if [[ $CI == true ]]; then cat ignore_gha_testing >> ignore_testing; fi'
     !buildhtml: bash -c 'find tutorials -name "*.md" | grep -vf ignore_testing | xargs jupytext --to notebook '
 
     !buildhtml: pytest --nbval-lax -vv --durations=10 tutorials