hotfix: Fix parsing pytorch verison (#1749)

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There was an issue in parsing the torch major version, so this PR fixes
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Author: sunghyunp-nvdia

flashinfer/jit/cpp_ext.py

@@ -25,7 +25,8 @@ def torch_get_pybind11_abi_build_flags() -> List[str]:
     # NOTE: starting from torch 2.9, this function is no longer needed
     # torch (cuda) version format is now like 2.9.0+cu129, so we need to split the version string
     # and check if the major version is at least 2.9
-    if Version(re.split(r"\+.*", torch.__version__)[0]) >= Version("2.9"):
+    torch_major_version = re.split(r"(\d+\.\d+)", torch.__version__)[1]
+    if Version(torch_major_version) >= Version("2.9"):
         return []
     else:
         abi_cflags = []