No longer run the plone.app.event tests.

Also, run the Python 3.11 tests with the latest Python 3.11, instead of a release candidate.

In the last two weekly cron tests, the plone tests fail with:

    ModuleNotFoundError: No module named 'plone.app.event'

I see the same locally.  I have no idea why.  But this seems a good time to stop running the `plone.app.event` tests within `icalendar`.

.github/workflows/tests.yml

@@ -23,8 +23,7 @@ jobs:
         - ["3.10",  "py310"]
         - ["pypy-3.9", "pypy3"]
         - ["3.10",  "docs"]
-        - ["3.10",  "plone"]
-        - ["3.11.0-rc.1",  "py311"]
+        - ["3.11",  "py311"]
 
     runs-on: ubuntu-latest
     name: ${{ matrix.config[1] }}

CHANGES.rst

@@ -6,7 +6,7 @@ Changelog
 
 Minor changes:
 
-- ...
+- No longer run the ``plone.app.event`` tests.
 
 Breaking changes:
 

tox.ini

@@ -1,6 +1,6 @@
 # to run for a specific environment, use ``tox -e ENVNAME``
 [tox]
-envlist = py37,py38,py39,py310,pypy3,docs,plone
+envlist = py37,py38,py39,py310,py311,pypy3,docs
 # Note: the 'docs' env creates a 'build' directory which may interfere in strange ways
 # with the other environments.  You might see this when you run the tests in parallel.
 # See https://github.com/collective/icalendar/pull/359#issuecomment-1214150269
@@ -23,17 +23,3 @@ changedir = docs
 allowlist_externals = make
 commands =
     make html
-
-[testenv:plone]
-usedevelop = False
-install = False
-python = 3.10
-commands_pre =
-# Install Plone and explicitly the single package that uses icalendar, plus the test runner.
-    pip install Plone plone.app.event[test] zope.testrunner -c https://dist.plone.org/release/6.0-dev/constraints.txt
-# Install the dev version of the package, mostly so we can safely point to the path with the tests.
-    pip install -e "git+https://github.com/plone/plone.app.event.git\#egg=plone.app.event"
-# icalendar is pinned in the constraints, but we want the current dev version.
-    pip install -e {toxinidir}
-commands =
-    zope-testrunner --test-path={envdir}/src/plone-app-event {posargs:-vc}