docker_appimage_tests.sh: simplify

add the version unconditionally in the script and do not add a placeholder
to Dockerfile

Author: MartinPulec

.github/scripts/Linux/docker_appimage_tests.sh

@@ -3,17 +3,12 @@
 mkdir aitest-context # empty build context
 ./UltraGrid-"$VERSION"-x86_64.AppImage --appimage-extract
 
-for n in archlinux ubuntu:22.04 ubuntu:latest; do
-        dockerfile=.github/scripts/Linux/utils/Dockerfile.$n
-        if expr $n : ".*:"; then
-                image_name=$(echo $n | cut -d: -f 1)
-                image_version=$(echo $n | cut -d: -f 2)
-                n_dockerfile=$(mktemp)
-                cat .github/scripts/Linux/utils/Dockerfile."$image_name" |
-                        sed "s/DOCKER_IMAGE_VERSION/$image_version/"\
-                        > "$n_dockerfile"
-                dockerfile=$n_dockerfile
-        fi
+for n in archlinux:latest ubuntu:22.04 ubuntu:latest; do
+        image_name=$(echo $n | cut -d: -f 1)
+        image_version=$(echo $n | cut -d: -f 2)
+        dockerfile=$(mktemp)
+        cat .github/scripts/Linux/utils/Dockerfile."$image_name" |
+                sed "/FROM /s/:\$/$image_version/" > "$dockerfile"
         docker build -f "$dockerfile" -t aitest-$n aitest-context
         docker run --rm -v "$PWD"/squashfs-root/:/AppImage aitest-$n sh -ce '
 /AppImage/AppRun -v

.github/scripts/Linux/utils/Dockerfile.ubuntu

@@ -1,6 +1,6 @@
 # inspired by https://github.com/aferrero2707/appimage-testsuite
 # installing libraries included in https://raw.githubusercontent.com/probonopd/AppImages/master/excludelist
-FROM ubuntu:DOCKER_IMAGE_VERSION
+FROM ubuntu
 RUN apt-get update
 RUN apt-get install -y libasound2 libegl1-mesa libfontconfig1 libgl1-mesa-glx \
     libgmp10 libharfbuzz0b libopengl0 libp11-kit0 libx11-6 xvfb