check_names: Use the same Python executable instead of `python3`

Fix build failure in environments where `python3` doesn't exist or is too
old.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/check_names.py

diff --git a/scripts/check_names.py b/scripts/check_names.py
index 9eab8cf..bdbeefd 100755
--- a/scripts/check_names.py
+++ b/scripts/check_names.py
@@ -850,7 +850,7 @@
             # Use check=True in all subprocess calls so that failures are raised
             # as exceptions and logged.
             subprocess.run(
-                ["python3", "scripts/config.py", "full"],
+                [sys.executable, "scripts/config.py", "full"],
                 universal_newlines=True,
                 check=True
             )
@@ -1019,7 +1019,7 @@
             # Use check=True in all subprocess calls so that failures are raised
             # as exceptions and logged.
             subprocess.run(
-                ["python3", "scripts/config.py", "full"],
+                [sys.executable, "scripts/config.py", "full"],
                 universal_newlines=True,
                 check=True
             )