Use UTF-8 for reading/writing sarif file

[explunit]

This PR adjusts the reading/writing of sarif files to use utf-8 encoding.

Before this change, I had to add this to my adjust-cvss step:

      env:
        PYTHONUTF8: "1"
        PYTHONIOENCODING: "UTF-8"

Otherwise I get an error like this:

UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 297884: character maps to <undefined>

It appears to be using cp1252. Here's the full trace

Traceback (most recent call last):
  File "D:\a\_actions\advanced-security\adjust-cvss\74da0f04ca3a1d2cbfcf140bf49a2039a783800a\adjust_cvss.py", line 122, in <module>
    main()
  File "D:\a\_actions\advanced-security\adjust-cvss\74da0f04ca3a1d2cbfcf140bf49a2039a783800a\adjust_cvss.py", line 119, in main
    adjust_cvss(args)
  File "D:\a\_actions\advanced-security\adjust-cvss\74da0f04ca3a1d2cbfcf140bf49a2039a783800a\adjust_cvss.py", line 55, in adjust_cvss
    s = json.load(f)
  File "C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\json\__init__.py", line 293, in load
    return loads(fp.read(),
  File "C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x9d in position 297884: character maps to <undefined>

Note that the job also has runs-on: windows-latest