Use wp_safe_remote_get() to retreive remote .ics data

[EvanHerman]

Description

The .ics parser was using fetch() to retrieve remote .ics file data. This PR uses wp_safe_remote_get() when retrieving remote .ics file data instead and removes any reference to fetch() since we do not allow local .ics files to be used.

Additional changes to the Ci/CD workflow:

• Updated .nvmrc to 18 to use Node v18 in the workflows
• Updated @wordpress/env to 10.1.0
• Updated @wordpress/scripts to 28.1.0
• Added WordPress 6.5 to the e2e test job

Screenshots

Types of changes

Bug fix (non-breaking change which fixes an issue)

How has this been tested?

Tested retrieving a remote .ics file from a Github account. (Note: The .ics file must have events in the future, or current day. If they have passed, they will not show up)

Acceptance criteria

Use wp_safe_remote_get() instead of fetch() to retrieve remote .ics file data, and ensure things still work as it does in its current state.

Checklist:

• My code is tested
• My code follows accessibility standards
• My code has proper inline documentation
• I've added proper labels to this pull request

[AnthonyLedesma]

Great work!