Accessibility issue in progress bar for pages that are not episodes: aria-valuenow="NA" - Invalid state or property

[josenino95]

An ARIA state or property has an invalid value. It may have been mistyped.

Occurrences (1 in each page)
From my understanding of the SiteImprove report, the issue arises from the aria-valuenow property of the progress bar when it is set to the value of "NA".

I see this happening in the following pages:

• reference.html
• discuss.html
• CODE_OF_CONDUCT.html
• LICENSE.html
• resources.html
• any additional pages that are not episodes, for example this "Further Exercises" page in the SC Python lesson: https://swcarpentry.github.io/python-novice-gapminder/exercises.html

<div class="progress software">
<div class="progress-bar software" role="progressbar" aria-valuenow="NA" aria-label="Lesson Progress" aria-valuemin="0" aria-valuemax="100" style="width: NA%"></div>
</div>

Why is this an issue?
ARIA attributes provide information about the behavior of interactive elements. For example, they can be used to tell screen reader users whether a checkbox is checked (aria-checked=true) or unchecked (aria-checked=false).

Non-standard or misspelled values will not deliver the intended user experience and may even break the usability of the page.

WCAG 2.2: Understanding Success Criterion 4.1.2: Name, Role, Value
ARIA 1.2: 6.2.4 Value
Siteimprove Alfa: Technical documentation for rule SIA-R19

[froggleston]

It looks like this is required for conformance (whilst #199 and #200 are best practice only) so I'll work on this next.

[froggleston]

Fixed by adjusting sandpaper to only show progress bar when in episodic content (and therefore when there's a progress value): carpentries/sandpaper@c4be409