Bump docker image to use stable poetry version

changelog.d/13688.docker

@@ -0,0 +1 @@
+Update docker image to use a stable version of poetry.

docker/Dockerfile

@@ -46,17 +46,8 @@ RUN \
 
 # We install poetry in its own build stage to avoid its dependencies conflicting with
 # synapse's dependencies.
-# We use a specific commit from poetry's master branch instead of our usual 1.1.14,
-# to incorporate fixes to some bugs in `poetry export`. This commit corresponds to
-#    https://github.com/python-poetry/poetry/pull/5156 and
-#    https://github.com/python-poetry/poetry/issues/5141 ;
-# without it, we generate a requirements.txt with incorrect environment markers,
-# which causes necessary packages to be omitted when we `pip install`.
-#
-# NB: In poetry 1.2 `poetry export` will be moved into a plugin; we'll need to also
-# pip install poetry-plugin-export (https://github.com/python-poetry/poetry-plugin-export).
 RUN --mount=type=cache,target=/root/.cache/pip \
-  pip install --user "poetry-core==1.1.0a7" "git+https://github.com/python-poetry/poetry.git@fb13b3a676f476177f7937ffa480ee5cff9a90a5"
+  pip install --user "poetry==1.2.0"
 
 WORKDIR /synapse