[Fix] `install.sh`: fix POSIX compliance, printf format strings, and profile detection

- Use `=` instead of `==` for string comparison (POSIX compliance)
- Use `printf '%b'` instead of variable as format string (prevents `%` characters in paths from being interpreted as format specifiers)
- Fix `TRIED_PROFILE` to reference `PROFILE` instead of `NVM_PROFILE` which is known to be empty at that point

Bugs introduced in https://github.com/nvm-sh/nvm/commit/a24ff3e605d72ce9480b2fad2d4c93f0093fa306, https://github.com/nvm-sh/nvm/commit/b6f1c156da0a998442c1c0b638082390118085ce, and https://github.com/nvm-sh/nvm/commit/a461a0fffcd9163726f4d652ca974d97a1097356 (PR https://github.com/nvm-sh/nvm/pull/1605).