Update develop for 9.6.0

[daledupreez]

Changes proposed in this Pull Request:

This PR updates our changelog, readme, and version for 9.6.0 as follows:

• Add new 9.6.0 section in changelog.txt, and move entries for some post-9.5.0 PRs to the new section
• Bump version to 9.6.0-dev in package.json and package-lock.json
• Remove the 9.5.0 section from readme.txt
• Bump version in plugin header to 9.6.0-dev
• Bump tested versions for WordPress and WooCommerce in plugin header
• Bump WC_STRIPE_VERSION constant to 9.6.0

Testing instructions

Inspection on this should be sufficient, but I may be missing context as to what normal looks like after a release, so happy to resolve this in some other way!

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• Covered with tests (or have a good reason not to test in description ☝️)
• [N/A] Tested on mobile (or does not apply)

Changelog entry

• This Pull Request does not require a changelog entry. (Comment required below)

Changelog Entry Comment

Comment

Post merge

• [N/A] Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• [N/A] Added the needs docs label (or does not apply)
• [N/A] Included this PR in the Release Thread scope (or does not apply)

[annemirasol]

We have been doing the changelog/readme updates as part of post-release activities (PeNR48-ci-p2), but I don't see a reason to block this if we want it earlier.

Also, we haven't been bumping the post-release version to x.x.x-dev, but could be good practice to start.