GPL3 in sources

**Describe the bug**
There is a file licensed under GPL3 in the Catch2 sources: [tools/scripts/updateDocumentToC.py](https://github.com/catchorg/Catch2/blob/3e82ef9317d4bb43d81b660404db3c3c5880aa7d/tools/scripts/updateDocumentToC.py#L8)

The LICENSE.txt file in the project source states that the project is under the Boost license, but clearly it's not as simple as that.

**Expected behavior**
I suggest either removing non-boost-licensed files from the project or follow a system like https://reuse.software/ that allows for multiple licenses.