[Fix] install.sh: do not log when user has requested no profile modifications

[Tests] `install.sh`: add tests for PROFILE=/dev/null profile skip

Verify that when PROFILE="/dev/null" is set:
- The "Profile not found" warning is suppressed
- Profile modification is skipped as expected

Co-authored-by: Wes Todd <wes@wesleytodd.com>
Co-authored-by: Jordan Harband <ljharb@gmail.com>

install.sh

@@ -428,7 +428,10 @@ nvm_do_install() {
   COMPLETION_STR='[ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"  # This loads nvm bash_completion\n'
   BASH_OR_ZSH=false
 
-  if [ -z "${NVM_PROFILE-}" ] ; then
+  if [ "${PROFILE-}" = '/dev/null' ] ; then
+    # the user has specifically requested NOT to have nvm touch their profile
+    echo
+  elif [ -z "${NVM_PROFILE-}" ] ; then
     local TRIED_PROFILE
     if [ -n "${PROFILE}" ]; then
       TRIED_PROFILE="${NVM_PROFILE} (as defined in \$PROFILE), "