Use python3 as default interpreter for python scripts

[Rot127]

Your checklist for this pull request

• [ ] I've documented or updated the documentation of every API function and struct this PR changes.
• [ ] I've added tests that prove my fix is effective or that my feature works (if possible)

Detailed description

Should fix the broken CIFuzz job:

[100%] Built target cstool
+ cd /src/capstonenext/bindings/python
+ sed -i -e s/#print/print/ capstone/__init__.py
+ export CFLAGS=
+ CFLAGS=
+ export AFL_NOOPT=1
+ AFL_NOOPT=1
+ python setup.py install
Traceback (most recent call last):
  File "setup.py", line 219, in <module>
    long_description=open('README.txt', encoding="utf8").read(),
TypeError: 'encoding' is an invalid keyword argument for this function
2024-06-14 16:16:44,998 - root - ERROR - Building fuzzers failed.
2024-06-14 16:16:44,998 - root - ERROR - Error building fuzzers for (commit: 757faef5c44c8ded3c1fca5d6518f541613e9978, pr_ref: refs/pull/2387/merge).

After https://github.com/google/oss-fuzz/pull/12028 is merged. But this requires this one to be merged first.

Test plan

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Closing issues

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