Use Bash for all shell tasks

[kysrpex]

Set executable: /bin/bash for all ansible.builtin.shell tasks for predictability.

Only affects tasks in remap_user.yml, since this is the only file containing ansible.builtin.shell tasks.

Solves this problem (relatd to usegalaxy-eu/infrastructure-playbook#1057).

TASK [usegalaxy_eu.handy.os_setup : Compute user mapping using script.] ********************************************************************************************************************
fatal: [maintenance.galaxyproject.eu -> localhost]: FAILED! => {"changed": false, "cmd": "set -o pipefail;\n./remap_user.py \\\n     -e 0:root -e 1:bin -e 2:daemon -e 3:adm -e 4:lp -e 5:sync -e 6:shutdown -e 7:halt -e 8:mail -e 11:operator -e 12:games -e 14:ftp -e 65534:nobody -e 81:dbus -e 500:systemd-coredump -e 193:systemd-resolve -e 59:tss -e 998:polkitd -e 997:unbound -e 996:sssd -e 74:sshd -e 72:tcpdump -e 995:pesign -e 32:rpc -e 29:rpcuser -e 994:telegraf -e 993:chrony -e 1000:centos -e 999:galaxy -e 499:gluster -e 989:dnsmasq -e 498:saslauth -e 497:condor -e 107:qemu \\\n     -d 999:galaxy \\\n    | tail -n +2\n", "delta": "0:00:00.004574", "end": "2023-12-20 09:08:07.362578", "msg": "non-zero return code", "rc": 2, "start": "2023-12-20 09:08:07.358004", "stderr": "/bin/sh: 1: set: Illegal option -o pipefail", "stderr_lines": ["/bin/sh: 1: set: Illegal option -o pipefail"], "stdout": "", "stdout_lines": []}

[kysrpex]

@sanjaysrikakulam Since we have just discussed this, I merge without approval in GitHub.