Proposing a PR to fix a few small typos

[timgates42]

Issue Type

[x] Bug (Typo)

Steps to Replicate and Expected Behaviour

• Examine pyPdf/xmp.py and observe signifigance, however expect to see significance.
• Examine pyPdf/pdf.py and observe preceeding, however expect to see preceding.
• Examine pyPdf/pdf.py and observe optionnal, however expect to see optional.
• Examine pyPdf/xmp.py and observe keywrods, however expect to see keywords.
• Examine pyPdf/pdf.py and observe matricies, however expect to see matrices.
• Examine pyPdf/pdf.py and observe heigth, however expect to see height.
• Examine pyPdf/pdf.py and observe enviroment, however expect to see environment.
• Examine pyPdf/pdf.py and observe dimentions, however expect to see dimensions.
• Examine pyPdf/pdf.py and observe dictionnary, however expect to see dictionary.

Notes

Semi-automated issue generated by
https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

To avoid wasting CI processing resources a branch with the fix has been
prepared but a pull request has not yet been created. A pull request fixing
the issue can be prepared from the link below, feel free to create it or
request @timgates42 create the PR. Alternatively if the fix is undesired please
close the issue with a small comment about the reasoning.

https://github.com/timgates42/pyPdf/pull/new/bugfix_typos

Thanks.