[1.7.x] Fixed #22454 - Changed compatibility warning hint

The warning hint of `_check_test_runner` of 1.6 compatibility had a link
to a general release note. The link should be edited to refer the
relevant "Backwards incompatible changes in 1.6" section that documents
the cause and the possible solutions and workarounds of the warning.

Backport of 214d1e1b0f from master
[1.7.x] Fixed a test failure introduced by 214d1e1b0f.

Backport of 9bc377d7d0 from master
[1.7.x] Fixed #22464 - included contrib/gis/static in tarball

After switching to setuptools in commit 66f546b,
contrib/gis/static isn't included in tarball anymore, this commit adds
that path to be `recursive-include` in `MANIFEST.in`

Backport of bad4721b45 from master
[1.7.x] Fixed #22471 -- Corrected misprint in i18n docs

Backport of 54d5c37de6572eae57a66339bb38719e681cee82 from master.
[1.7.x] Added some missing items to the 1.6.3 release notes.

Backport of c2b269df6e from master
[1.7.x] Fixed #22399 -- Forced fixture reading in binary mode

This might help on systems where default encoding is not UTF-8 (and
on Python 3).
Thanks bacilla for the report.
Backport of ed532a6a1 from master.
[1.7.x] Adapted fixture read mode to file type

Binary mode added in ed532a6a1e is not supported by ZipFile.
Refs #22399.
Backport of 275811a93 from master.
[1.7.x] Fixed #22473 -- Emphasized that Model.clean() is not called from Model.save().

Backport of b43bbd6d39 from master
[1.7.x] Fixed #22472 -- Clarified meaning of dots in tutorial 4 code block.

Backport of 6b2ce38c49 from master
[1.7.x] Fixed #22458 -- Added a note about MySQL utf8_unicode_ci collation

Thanks tobami at gmail.com for the report.

Backport of 11ac50b18e from master
[1.7.x] Moved RemoteUserBackend documentation to reference guide.

Backport of 26d118c3fe from master
[1.7.x] Fixed #22397 -- Issues removing M2M field with explicit through model

Changed the migration autodetector to remove models last so that FK
and M2M fields will not be left as dangling references. Added a check
in the migration state renderer to error out in the presence of
dangling references instead of leaving them as strings. Fixed a bug
in the sqlite backend to handle the deletion of M2M fields with
"through" models properly (i.e., do nothing successfully).

Thanks to melinath for report, loic for tests and andrewgodwin and
charettes for assistance with architecture.

Backport of 956bd64424 from master