Pin tox to < 4.0.0

Tox 4.0.0 was recently released and it has several breaking changes.
We pin to < 4.0.0 here. We are planning to move forward only on the
master charm branches.

Tox is also pinned to < 4.0.0 for stable branches in upstream
openstack-zuul-jobs as well as in zosci-config. However, the
requires= section in the charm's tox.ini file ends up installing
tox>4, wiping out the zuul-pinned tox<4 that was already installed
installed. This patch fixes that.

Additional changes included in this patch:
- Cherry-pick from commit 24d557ffdc
  by hand.
- Add bindep.txt to install standard binary dependencies. These
  appear to no longer be required on master.
- Switch charm-tools to 2.8.4 to remove ruamel requirement that
  doesn't work on Python 3.10.

Related-Bug: #2002788
Change-Id: I231f6c19a574bb3f337451c98d2f7a8c0bafd65c

bindep.txt

@@ -0,0 +1,4 @@
+libffi-dev [platform:dpkg]
+libpq-dev [platform:dpkg]
+libxml2-dev [platform:dpkg]
+libxslt1-dev [platform:dpkg]

tests/bundles/jammy-yoga.yaml

@@ -17,9 +17,6 @@ machines:
   '5':
   '6':
   '7':
-  '8':
-    series: bionic  # nagios not supported on focal+ yet
-
 
 applications:
 

tox.ini

@@ -26,6 +26,7 @@ requires =
   pip < 20.3
   virtualenv < 20.0
   setuptools < 50.0.0
+  tox < 4.0.0
 
 # NOTE: https://wiki.canonical.com/engineering/OpenStack/InstallLatestToxOnOsci
 minversion = 3.18.0
@@ -84,7 +85,7 @@ deps = -r{toxinidir}/requirements.txt
 [testenv:pep8]
 basepython = python3
 deps = flake8==3.9.2
-       charm-tools==2.8.3
+       charm-tools==2.8.4
 commands = flake8 {posargs} hooks unit_tests tests actions lib files
            charm-proof