Previous `ScriptTestContext` might get overriden when concatenating `Map`s of `ScriptTestContext`s

Note that the `Map` here has `ScriptHash` as the key type:
```
instance AlonzoEraImp ConwayEra where
scriptTestContexts =
plutusTestScripts SPlutusV1
<> plutusTestScripts SPlutusV2
<> plutusTestScripts SPlutusV3
```

That means that whenever a new `plutusTestScripts` with a different language is concatenated to the map, the previous `ScriptTestContext` gets overwritten.