Repair commenting out pre-4.0 sct settings. (#3805)

This was inadvertently broken in #3591.

Fixes #3804

Co-authored-by: Joshua Newton <joshuacwnewton@gmail.com>

install_sct

@@ -717,7 +717,7 @@ conda deactivate >/dev/null 2>&1
 if [[ -e "$RC_FILE_PATH" ]]; then
     if grep "sct_env" "$RC_FILE_PATH"; then
       print info "In case an old version SCT is already installed (4.0.0-beta.1 or before), remove 'sct_env' declaration in RC file"
-      perl -pi -e '/sct_env/ s/^#*/#/' "$RC_FILE_PATH"
+      perl -pi -e 's/^(# )?(.*bin/sct_env)/# \2/' "$RC_FILE_PATH"
     fi
     if grep "^export MPLBACKEND=Agg" "$RC_FILE_PATH"; then
       print info "Commenting out 'export MPLBACKEND=Agg' from previous SCT installation"