add a showerror implementation for InvalidStateException (#41901)

Author: KristofferC

base/channels.jl

@@ -298,6 +298,7 @@ struct InvalidStateException <: Exception
     msg::String
     state::Symbol
 end
+showerror(io::IO, ex::InvalidStateException) = print(io, "InvalidStateException: ", ex.msg)
 
 """
     put!(c::Channel, v)

doc/src/manual/asynchronous-programming.md

@@ -211,7 +211,7 @@ A channel can be visualized as a pipe, i.e., it has a write end and a read end :
     julia> close(c);
 
     julia> put!(c, 2) # `put!` on a closed channel throws an exception.
-    ERROR: InvalidStateException("Channel is closed.",:closed)
+    ERROR: InvalidStateException: Channel is closed.
     Stacktrace:
     [...]
     ```
@@ -230,7 +230,7 @@ A channel can be visualized as a pipe, i.e., it has a write end and a read end :
     1
 
     julia> take!(c) # No more data available on a closed channel.
-    ERROR: InvalidStateException("Channel is closed.",:closed)
+    ERROR: InvalidStateException: Channel is closed.
     Stacktrace:
     [...]
     ```