CI: Add mypy check

Signed-off-by: Stefan Hansson <newbyte@postmarketos.org>
Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/7960>

.ci/mypy.sh

@@ -0,0 +1,16 @@
+#!/bin/sh -e
+# Description: static type checking for python scripts
+# https://postmarketos.org/pmb-ci
+
+if [ "$(id -u)" = 0 ]; then
+	set -x
+	apk -q add py3-argcomplete py3-pip py3-pytest
+	exec su "${TESTUSER:-build}" -c "sh -e $0"
+fi
+
+set -x
+
+pip install --break-system-packages --no-warn-script-location mypy
+# Need to change directory for pyproject.toml to be picked up.
+cd .ci
+python -m mypy .

.ci/pyproject.toml

@@ -0,0 +1,2 @@
+[tool.mypy]
+disable_error_code = ["import-not-found"]

.gitlab-ci.yml

@@ -62,6 +62,18 @@ ruff:
     - .ci/lib/gitlab_prepare_ci.sh
     - .ci/ruff.sh
 
+# testcases typechecking
+mypy:
+  stage: lint
+  rules:
+    - if: *mr_rule
+      changes:
+        - .ci/**/*
+        - .gitlab-ci.yml
+  script:
+    - .ci/lib/gitlab_prepare_ci.sh
+    - .ci/mypy.sh
+
 # shellcheck and various grep checks
 shellcheck-grep:
   stage: lint