Hello,

I found an issue with fish shell code blocks, in that the `:var' parameter generates a command that is not syntaxically correct. Fish uses `set variable value' instead of `variable = value'. As a result, org-babel throws an error when executing the code block. This patch fixes this by adding an exception to org-babel-variable-assignments:shell on the model of what it already does for bash.

Example of code block triggering the error:
#+begin_src fish :var test
echo $test
#+end_src

Best regards,
Elias