minor #121 Add a failing test about titles using non-Latin scripts (javiereguiluz)

This PR was squashed before being merged into the main branch.

Discussion
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Add a failing test about titles using non-Latin scripts

Title says it all. The problem is in this line:

https://github.com/doctrine/rst-parser/blob/35c61ece3a209a742f9382a4b4f5680365979750/lib/Environment.php#L492

```
iconv(): Detected an illegal character in input string

vendor/doctrine/rst-parser/lib/Environment.php:492
vendor/doctrine/rst-parser/lib/Nodes/TitleNode.php:32
vendor/doctrine/rst-parser/lib/NodeFactory/NodeInstantiator.php:71
vendor/doctrine/rst-parser/lib/NodeFactory/DefaultNodeFactory.php:272
vendor/doctrine/rst-parser/lib/NodeFactory/DefaultNodeFactory.php:83
vendor/doctrine/rst-parser/lib/Parser/DocumentParser.php:481
vendor/doctrine/rst-parser/lib/Parser/DocumentParser.php:395
vendor/doctrine/rst-parser/lib/Parser/DocumentParser.php:212
vendor/doctrine/rst-parser/lib/Parser/DocumentParser.php:149
vendor/doctrine/rst-parser/lib/Parser.php:178
vendor/doctrine/rst-parser/lib/Parser.php:162
vendor/doctrine/rst-parser/lib/Parser.php:200
tests/IntegrationTest.php:99
```

Should I create a PR in Doctrine RST parser to add Symfony String as a dependency and slugify strings with it?

Commits
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8fe50b1 Add a failing test about titles using non-Latin scripts

Author: javiereguiluz

composer.json

@@ -14,6 +14,7 @@
         }
     },
     "require": {
+        "php": "^7.2 || ^8.0",
         "ext-json": "*",
         "ext-curl": "*",
         "doctrine/rst-parser": "^0.4",