fix: remove use of SHELL and specify bash in RUN

Remove the use of the `SHELL` command as it is not part of the OCI
specification.

Specify the use of `bash` in the `RUN` HEREDOC

Author: JohnVillalovos

Dockerfile

@@ -23,10 +23,9 @@ COPY --from=comp /usr/bin/composer /usr/bin/composer
 
 # Update and install required debian packages
 ENV DEBIAN_FRONTEND=noninteractive
-SHELL ["/bin/bash", "-o", "pipefail", "-c"]
 # hadolint ignore=DL3008 # 'Pin versions in apt get install'
-RUN <<EORUN
-set -xeu
+RUN <<EORUN bash
+set -xeuo pipefail
 apt-get update
 apt-get upgrade --yes
 apt-get install --yes --no-install-recommends \
@@ -42,8 +41,8 @@ rm -rf /var/lib/apt/lists/*
 EORUN
 
 # Customize the http & php environment
-RUN <<EORUN
-set -xeu
+RUN <<EORUN bash
+set -xeuo pipefail
 cp "$PHP_INI_DIR/php.ini-production" "$PHP_INI_DIR/php.ini"
 cat > /etc/apache2/conf-available/remoteip.conf <<EOF
 RemoteIPHeader X-Real-IP
@@ -75,8 +74,8 @@ EORUN
 # Get and customize librebooking
 ARG APP_GH_REF
 ARG APP_GH_ADD_SHA=false
-RUN <<EORUN
-set -xeu
+RUN <<EORUN bash
+set -xeuo pipefail
 LB_TARBALL_URL="https://api.github.com/repos/LibreBooking/librebooking/tarball/${APP_GH_REF}"
 curl \
   --fail \