[Bug]: handle backtick in variable interpolation

[SimoneBergonzi]

What version or versions you have tested?

1.2.3

Which operating systems have you used?

• macOS
• Windows
• Linux

What did you expect to happen?

I would like the possibility to use backticks in variables which I interpolate with mlp

What happened instead?

I have a variable with a backtick that is not correctly handled in the interpolation, it leads to a MalformedYAMLError

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