CI: mypy: make compatible with "pmbootstrap ci" (MR 29)

.ci/mypy.sh

+#!/bin/sh -e
+# Description: static type checking for python scripts
+# https://postmarketos.org/pmb-ci
+
+if [ "$(id -u)" = 0 ]; then
+	set -x
+	apk -q add py3-argcomplete py3-mypy
+	exec su "${TESTUSER:-build}" -c "sh -e $0"
+fi
+
+set -x
+
+mypy mrhlpr.py mrtest.py

.gitlab-ci.yml

@@ -8,6 +8,6 @@ flake8:
   - .ci/flake8.sh
 mypy:
   before_script:
-  - apk add py3-argcomplete py3-mypy
+  - adduser -D build
   script:
-  - mypy mrhlpr.py mrtest.py
+  - .ci/mypy.sh