Closes #1451

This sets the test suite to use ubuntu-20.04 as opposed to ubuntu-latest as the latter switched over in the last day or so to using ubuntu-22.04 and that broke testing Python 3.6. Ubuntu 20.04 has maintenance fixes for another ~2.5 years, and is supported critically for another 5 years after that

Signed-off-by: Matthew Peveler <matt.peveler@gmail.com>

Signed-off-by: Matthew Peveler <matt.peveler@gmail.com>

Also fix various type annotations

Applies to merge/append

This currently returns only an empty list . Pending to  PR#1371

This PR ensures PyPDF2 uses page_number instead of pagenum as a parameter name.

* It does not touch functions that are deprecated anyway.
* The position of the new parameter is the same as the old one
* The old parameter name is added to ensure that people who use the keyword-parameter don't have a breaking change.

Credits to @mtd91429 who pointed out those inconsistencies in #1187

Fixes #1474

Fixes #1221

Credit goes to Alper Ahmetoglu for the fix

Co-authored-by: Alper Ahmetoglu <ahmetoglu.alper@gmail.com>

* Update docs.txt to 3.7 as https://readthedocs.io/ seems to use 3.7
* Update dev.txt to 3.7 as we cannot expect developers to use a deprecated Python version (although we still keep it in CI and want to keep compatibility if possible)

PDF annotations - for example hyperlinks and comments - were not properly scaled when using the scale function.

Fixes #1386

New Features (ENH):
-  Add support to extract gray scale images (#1460)
-  Add 'threads' property to PdfWriter (#1458)
-  Add 'open_destination' property to PdfWriter (#1431)
-  Make PdfReader.get_object accept integer arguments (#1459)

Bug Fixes (BUG):
-  Scale PDF annotations (#1479)

Robustness (ROB):
-  Padding issue with AES encryption (#1469)
-  Accept empty object as null objects (#1477)

Documentation (DOC):
-  Add module documentation the PaperSize class (#1447)

Maintenance (MAINT):
-  Use 'page_number' instead of 'pagenum' (#1365)
-  Add List of pages to PageRangeSpec (#1456)

Testing (TST):
-  Cleanup temporary files (#1454)
-  Mark test_tounicode_is_identity as external (#1449)
-  Use Ubuntu 20.04 for running CI test suite (#1452)

[Full Changelog](2.11.2...2.12.0)