using PyPlot hangs/kills julia 1.8.5 or 1.9.0 on MacOS

## using PyPlot hangs or kills julia 1.8.5 or 1.9.0 on MacOS

### Synopsis
`using PyPlot` hangs julia. No progress for >10 hours. No error message. User `^C` exits julia with `Killed: 9`.

With repeated testing, behavior has evolved to crash immediately with `Killed: 9`, where it had hung.

### Demonstration
Carefully recursively force-removed the conda directory `$HOME/.julia/conda`, which seems to be shared between julia 1.8 and 1.9.

Start julia, making sure dynamic dependencies are consistent with the conda python installation.
```
LD_LIBRARY_PATH="$HOME/.julia/conda/3/lib" /Applications/Julia-1.8.app/Contents/Resources/julia/bin/julia
```
or
```
LD_LIBRARY_PATH="$HOME/.julia/conda/3/lib" /Applications/Julia-1.9.app/Contents/Resources/julia/bin/julia
```

Make sure julia is using the conda python distribution and build PyCall.
```julia
ENV["PYTHON"]=""
]build PyCall
Building Conda ─→ `~/.julia/scratchspaces/44cfe95a-1eb2-52ea-b672-e2afdf69b78f/e32a90da027ca45d84678b826fffd3110bb3fc90/build.log`
Building PyCall → `~/.julia/scratchspaces/44cfe95a-1eb2-52ea-b672-e2afdf69b78f/62f417f6ad727987c755549e9cd88c46578da562/build.log`
...
```

Quit and restart julia, then run
```julia
using PyPlot
```

Since we started by wiping `~/.julia/conda`, matplotlib is not installed. Conda is automatically deployed to install it:
```
[ Info: Installing matplotlib via the Conda matplotlib package...
[ Info: Running `conda install -y matplotlib` in root environment
...
Executing transaction: done
```
It hangs there.

Kill julia with ^C -> `Killed: 9`.

Try again now that matplotlib is installed:
```
LD_LIBRARY_PATH="$HOME/.julia/conda/3/lib" /Applications/Julia-1.8.app/Contents/Resources/julia/bin/julia
ENV["PYTHON"]=""
using PyPlot
```
Result: It just hangs immediately. So, I think probably conda installs matplotlib (maybe OK?), but julia is unable to use it.

I have to kill julia with ^C -> `Killed: 9`.

Trying again.
```
LD_LIBRARY_PATH="$HOME/.julia/conda/3/lib" /Applications/Julia-1.8.app/Contents/Resources/julia/bin/julia
ENV["PYTHON"]=""
using Conda # returns
using PyCall # returns
using PyPlot # crashes
Killed: 9
```
Crashes and exits.

Even wiping `.julia/conda` again, it just crashes now with `Killed: 9`

### Background
PyPlot had previously been working for me.
The first sign of trouble was an MKL dylib conflict error message and crash when running `using PyPlot`.
Unfortunately after many ^Cs I can't find that error message.

I updated julia's conda after that. Then I got the behavior reported above.

使用提供的 Julia 1.8/1.9 启动命令、LD_LIBRARY_PATH，以及在 macOS 上依次执行 `using Conda`、`using PyCall` 和 `using PyPlot`，重现该故障。检查报告中的 Conda matplotlib 安装以及之前的 MKL dylib 冲突；当 `using PyPlot` 完成且未发生挂起或以 `Killed: 9` 退出时，即表示完成。

由索引模型根据 Issue 内容生成。