Calling ElementTree.write on an ElementTree instance where ElementTree._root is the wrong type causes possible data loss

[abstractedfox]

Bug report

Bug description:

Example:

tree = xml.etree.ElementTree.ElementTree(element = "") # element should be an ElementTree.Element object or None
tree.write("file.xml") # This appropriately causes a traceback, but blanks file.xml if it exists

PR coming with a fix!

CPython versions tested on:

CPython main branch, 3.14

Operating systems tested on:

macOS

Linked PRs

• gh-135640: Adds type checking to ElementTree.ElementTree constructor #135643
• [3.14] gh-135640: Adds more type checking to ElementTree (GH-135643) #136225
• [3.13] gh-135640: Adds more type checking to ElementTree (GH-135643) #136226