the block revision is not increased after joining two blocks in a QPlainTextEdit

tldr: see attached testcase

Steps to reproduce:

• create a QPlainTextEdit
• set text with more than one line, for example: "line1\nline2"
• move the text cursor to the end of the first line
• press del to remove the line break

Expected result:

• the first line QTextBlock::revision() before and after removing the line break differ

Current result:

• the first line QTextBlock::revision() before and after removing the line break is identical