FIX - Upload documentation only when merging to main

[Badr-MOUFAD]

Context of the PR

Follow up on #206,
In Circleci jobs, the last instructions aren't meant to run if we merge to main

skglm/.circleci/config.yml

Lines 85 to 94 in c67a885

	# Add stable documentation
	- run:
	name: stable_doc
	command: |
	set -e
	mkdir -p ~/.ssh
	echo -e "Host *\nStrictHostKeyChecking no" > ~/.ssh/config
	chmod og= ~/.ssh/config
	cd doc;
	make add-stable-doc

since these are already performed in the Deploy step.

Therefore the CI fails (although everything is fine)

Contributions of the PR

• upload documentation to gh-pages if the branch is main

Checks before merging PR

• [ ] added documentation for any new feature
• [ ] added unittests
• [ ] edited the what's new