CI PR #2: Fix GitHub CI and add checks to compensate for code coverage

[bernhardkaindl]

@chunjiez, @stephenchengCloud, this PR helps to prepare for the next PRs (#145 is next) to fix running CI (tox, pre-commit)

Contents:

• Fix the required code coverage by extending the unit tests to cover the missing lines.
• Fix two spelling typos in the comments

[coveralls]

Pull Request Test Coverage Report for Build 11858778149

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 12 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.009%) to 83.661%

---

Files with Coverage Reduction	New Missed Lines	%
xcp/accessor.py	1	89.1%
xcp/xmlunwrap.py	2	92.31%
xcp/cpiofile.py	3	75.26%
xcp/compat.py	6	78.57%

Totals
Change from base Build 9109272969:	-0.009%
Covered Lines:	2806
Relevant Lines:	3354

---

💛 - Coveralls