Backport of odoo/addons/base/tests/minimal.pdf

Our updated version of PyPDF2 (1.27.12) has broken TestPdf tests
with PyPDF2.errors.PdfReadError: Broken xref table.

It turns out this is a novel behavior that does not happen with
PyPDF2 version used by vanilla Odoo 14 which is 1.26.0.

The upstream commit 07297fb has
updated the test PDF file (odoo/addons/base/tests/minimal.pdf) for
which the mentioned xref exception is not raised anymore.

For the backport, the test case test_download_one_corrupted_pdf
also had to be adapted a little bit.

odoo/addons/base/tests/test_pdf.py

@@ -104,8 +104,8 @@ def test_download_one_corrupted_pdf(self):
         """
         attach_name = 'super_attach.pdf'
         # we need to corrupt the file: change count object in the xref table
-        pattern = re.compile(r"xref\n\d\s+(\d)")
-        corrupted_file = re.sub(pattern, "xref\n0 5", self.file.decode('utf-8'), 1).encode('utf-8')
+        pattern = re.compile(rb"xref\n\d\s+(\d)")
+        corrupted_file = re.sub(pattern, b"xref\n0 5", self.file, 1)
 
         self.env['ir.attachment'].create({
             'datas': base64.b64encode(corrupted_file),