fix EESSI prefix for complex prompts

[smoors]

my prompt looks like this:

$(if [ $? != 0 ]; then echo '\[\e[0;31m\]'✘ '\[\e[0m\]'; else echo '\[\e[0;32m\]'✔ '\[\e[0m\]'; fi)\[\033[33m\][$(date '+%H:%M')]\[\033[00m\] \u@\h \[\033[01;34m\]$(fixpathvsc)\[\033[00m\] \$ $(__git_ps1 "(%s) ")$(test $(id -gn) != "vsc10009" && echo "($(id -gn)) ")

before this PR, it results in an error and a hanging shell after unloading the EESSI module:

✔ [20:21] vsc10009@login1 $VSC_HOME $ source /cvmfs/software.eessi.io/versions/2025.06/init/lmod/bash
Modules purged before initialising EESSI
Module for EESSI/2025.06 loaded successfully
EESSI has selected x86_64/intel/skylake_avx512 as the compatible CPU target for EESSI/2025.06
EESSI did not identify an accelerator on the system
(for debug information when loading the EESSI module, set the environment variable EESSI_MODULE_DEBUG_INIT)
{EESSI/2025.06} ✔ [20:21] vsc10009@login1 $VSC_HOME $ ml unload EESSI/2025.06                                                                                                                      
-bash: command substitution: line 3: unexpected EOF while looking for matching `"'                                                                                                                 
-bash: command substitution: line 4: syntax error: unexpected end of file
-bash: command substitution: line 1: unexpected EOF while looking for matching `)'
-bash: command substitution: line 2: syntax error: unexpected end of file