Install Singularity 3 from official DEB

.appveyor.yml

@@ -64,7 +64,7 @@ environment:
     - ID: Ubu20
       DTS: datalad_container
       APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu2004
-      INSTALL_SYSPKGS: python3-virtualenv xz-utils singularity-container
+      INSTALL_SYSPKGS: python3-virtualenv xz-utils jq
       # system git-annex is way too old, use better one
       INSTALL_GITANNEX: git-annex -m deb-url --url http://snapshot.debian.org/archive/debian/20210906T204127Z/pool/main/g/git-annex/git-annex_8.20210903-1_amd64.deb
       CODECOV_BINARY: https://uploader.codecov.io/latest/linux/codecov
@@ -158,6 +158,8 @@ install:
   - sh: "[ \"$ID\"x = \"Ubu20x\" ] && wget -O- http://neuro.debian.net/lists/focal.us-nh.full | sudo tee /etc/apt/sources.list.d/neurodebian.sources.list && ( sudo apt-key adv --recv-keys --keyserver hkps://keyserver.ubuntu.com 0xA5D32F012649A5A9 || { wget -q -O- http://neuro.debian.net/_static/neuro.debian.net.asc | sudo apt-key add -; } )"
   # Missing system software
   - sh: "[ -n \"$INSTALL_SYSPKGS\" ] && ( [ \"x${APPVEYOR_BUILD_WORKER_IMAGE}\" = \"xmacOS\" ] && brew install -q ${INSTALL_SYSPKGS} || { sudo apt-get update -y -qq && sudo apt-get install -qq --no-install-recommends -y ${INSTALL_SYSPKGS}; } ) || true"
+  # Install singularity
+  - sh: tools/ci/install-singularity.sh
   # Install git-annex on windows, otherwise INSTALL_SYSPKGS can be used
   # deploy git-annex, if desired
   - cmd: IF DEFINED INSTALL_GITANNEX datalad-installer --sudo ok %INSTALL_GITANNEX%

.travis.yml

@@ -42,8 +42,9 @@ before_install:
   # no recommends to avoid inheriting the entire multimedia stack
   - travis_retry sudo eatmydata apt-get install --no-install-recommends git-annex-standalone aria2 git-remote-gcrypt lsof gnupg nocache
   # chroot/container stuff
-  - travis_retry sudo eatmydata apt-get install xz-utils singularity-container
+  - travis_retry sudo eatmydata apt-get install xz-utils jq
   - pip install --upgrade pip
+  - tools/ci/install-singularity.sh
 
 
 install:

tools/ci/install-singularity.sh

@@ -0,0 +1,8 @@
+#!/bin/bash
+
+release="$(curl -fsSL https://api.github.com/repos/sylabs/singularity/releases/latest | jq -r .tag_name)"
+codename="$(lsb_release -cs)"
+arch="$(dpkg --print-architecture)"
+wget -O /tmp/singularity-ce.deb https://github.com/sylabs/singularity/releases/download/$release/singularity-ce_${release#v}-${codename}_$arch.deb
+sudo dpkg -i /tmp/singularity-ce.deb
+sudo apt-get install -f