Handle async functions in bind

[philippjfr]

Partially fixes #3262

[codecov]

Codecov Report

Merging #3264 (a9c53ca) into master (11d4637) will decrease coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #3264      +/-   ##
==========================================
- Coverage   83.17%   83.14%   -0.03%     
==========================================
  Files         195      195              
  Lines       26021    26030       +9     
==========================================
+ Hits        21642    21643       +1     
- Misses       4379     4387       +8     

Impacted Files	Coverage Δ
panel/depends.py	80.51% <66.66%> (-3.31%)	⬇️
panel/io/callbacks.py	80.67% <0.00%> (-3.37%)	⬇️

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