CI: Use install_mypy.sh

Reduces repetition.

.ci/mypy.sh

@@ -4,7 +4,8 @@
 
 if [ "$(id -u)" = 0 ]; then
 	set -x
-	apk -q add py3-argcomplete py3-gitlab py3-mypy
+	wget https://gitlab.postmarketos.org/postmarketOS/ci-common/-/raw/master/install_mypy.sh
+	sh ./install_mypy.sh py3-argcomplete py3-gitlab
 	exec su "${TESTUSER:-build}" -c "sh -e $0"
 fi
 

.ci/native-build.sh

@@ -4,14 +4,11 @@
 
 if [ "$(id -u)" = 0 ]; then
 	set -x
-	apk -q add gcc musl-dev py3-argcomplete py3-gitlab py3-pip python3-dev
+	wget https://gitlab.postmarketos.org/postmarketOS/ci-common/-/raw/master/install_mypy.sh
+	sh ./install_mypy.sh py3-argcomplete py3-gitlab --with-mypyc
 	exec su "${TESTUSER:-build}" -c "sh -e $0"
 fi
 
 set -x
 
-# mypyc from Alpine may be an old version. Given mypyc's early development
-# status, install it from pypi instead to ensure we don't have to deal with
-# working around bugs that already have been fixed in newer versions.
-pip install --break-system-packages --no-warn-script-location mypy
 python -m mypyc mrtest mrhlpr
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