Fix python_requires versioning for new setuptools

Newer versions of setuptools will fail to install LNT with the following error:

```
× python setup.py egg_info did not run successfully.
  │ exit code: 1
  ╰─> [1 lines of output]
      error in LNT setup command: 'python_requires' must be a string containing valid version specifiers; Invalid specifier: '>=3.6.*'
      [end of output]
```

From reading the documentation, I believe it was a bug to allow >=3.6.* previously, as I don't think wild cards are supported here
https://peps.python.org/pep-0345/#requires-python

Patch by Justice Adams!

1 files changed, 1 insertions, 1 deletions

diff --git a/setup.py b/setup.py
index 690da0c..de46afb 100644
--- a/setup.py
+++ b/setup.py
@@ -138,5 +138,5 @@ The *LNT* source is available in the llvm-lnt repository:
 
     ext_modules=[cPerf],
 
-    python_requires='>=3.6.*',
+    python_requires='>=3.6',
 )