Devops: Do not pin the mamba version (#6466)

* Remove pin of mamba version
* Set `PIP_USER` as default
* Remove double install of `xz-utils`

.docker/aiida-core-base/Dockerfile

@@ -104,9 +104,6 @@ USER ${SYSTEM_UID}
 # Pin python version here
 ARG PYTHON_VERSION
 
-# Pin mamba version here
-ARG MAMBA_VERSION
-
 # Download and install Micromamba, and initialize Conda prefix.
 #   <https://github.com/mamba-org/mamba#micromamba>
 #   Similar projects using Micromamba:
@@ -137,7 +134,7 @@ RUN set -x && \
         --prefix="${CONDA_DIR}" \
         --yes \
         "${PYTHON_SPECIFIER}" \
-        "mamba=${MAMBA_VERSION}" && \
+        mamba && \
     rm micromamba && \
     # Pin major.minor version of python
     mamba list python | grep '^python ' | tr -s ' ' | cut -d ' ' -f 1,2 >> "${CONDA_DIR}/conda-meta/pinned" && \
@@ -146,8 +143,9 @@ RUN set -x && \
     fix-permissions "/home/${SYSTEM_USER}"
 
 # Add ~/.local/bin to PATH where the dependencies get installed via pip
-# This require the package installed with `--user` flag in pip
+# This require the package installed with `--user` flag in pip, which we set as default.
 ENV PATH=${PATH}:/home/${SYSTEM_USER}/.local/bin
+ENV PIP_USER 1
 
 # Switch to root to install AiiDA and set AiiDA as service
 # Install AiiDA from source code

.docker/aiida-core-with-services/Dockerfile

@@ -22,8 +22,7 @@ RUN mamba install --yes \
 # Install erlang.
 RUN apt-get update --yes && \
      apt-get install --yes --no-install-recommends \
-     erlang \
-     xz-utils && \
+     erlang && \
      apt-get clean && rm -rf /var/lib/apt/lists/* && \
      # Install rabbitmq.
      wget -c --no-check-certificate https://github.com/rabbitmq/rabbitmq-server/releases/download/v${RMQ_VERSION}/rabbitmq-server-generic-unix-${RMQ_VERSION}.tar.xz && \

.docker/docker-bake.hcl

@@ -43,7 +43,6 @@ target "aiida-core-base" {
   platforms = "${PLATFORMS}"
   args = {
     "PYTHON_VERSION" = "${PYTHON_VERSION}"
-    "MAMBA_VERSION" = "1.5.2"
   }
 }
 target "aiida-core-with-services" {