Fix: Branch Param As String

[ax3l]

Branches should always be a string, otherwise tags like 21.12 are parsed as floats, which leads to errors such as:

  File "regression_testing/repo.py", line 38, in get_branch_name
    return self.branch_wanted.strip("\"")
AttributeError: 'float' object has no attribute 'strip'

[zingale]

good catch