Upgrade Enketo to 7.6.4

[lognaturel]

Closes #1885 Closes #2071

Because the Enketo default map config does not set referrerPolicy, we need to add a map config block.

What has been done to verify that this works as intended?

Upgraded to 7.6.4 on dev. Verified that Google Maps works. Verified that OSM with explicit referrerPolicy configuration works.

While doing this I noticed that OSM tiles don't work with an /x/ "offlineable" form. I see a NS_ERROR_INTERCEPTION_FAILED error. This happens with 7.6.1 as well so I don't think we need to do anything about it. Cloud is unaffected because it uses Google Maps.

Why is this the best possible solution? Were any other approaches considered?

I considered seeing whether we should add referrerPolicy to the default Enketo maps config but I think this is ok.

How does this change impact users? Describe intentional behavior changes from code updates. What are the regression risks?

I looked at the Enketo release notes and associated code changes and I think they're overall low-risk. The dynamic read-only doesn't appear to be complete (e.g. dates don't become read-only) but that's no worse than it was before.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No. Enketo docs have been updated for self-hosters who manage their own config.

[lognaturel]

Added @sadiqkhoja in case @alxndrsn doesn't have a chance to review. Would be great to get this on staging asap.

[alxndrsn]

Useful comparisons:

• github: enketo/enketo@7.6.1...7.6.4
• git cli (full changes):

git diff 7.6.1 7.6.4

• git cli (commits):

git log 7.6.1..7.6.4

[sadiqkhoja]

Discussed in the meeting to merge this and get this to staging so that this can be test.