add3prf.py: Support license files with extensions

Some crates place there license files in files with extensions, such as
LICENSE.txt or LICENSE-MIT.md.

We should account for extensions by removing them.

Bug: 321064939
Test: Ran script against `minimal-lexical-0.2.1` crate and added unit
      tests
Change-Id: I0c385e8209969c0900909e764460fc551f07c20c
diff --git a/scripts/add3prf.py b/scripts/add3prf.py
index 6f808ef..44a8418 100755
--- a/scripts/add3prf.py
+++ b/scripts/add3prf.py
@@ -193,8 +193,8 @@
   # Some crate like time-macros-impl uses lower case names like LICENSE-Apache.
   licenses = []
   license_file = None
-  for license_file in glob.glob("LICENSE*") + glob.glob("COPYING*") + glob.glob("UNLICENSE"):
-    lowered_name = license_file.lower()
+  for license_file in glob.glob("LICENSE*") + glob.glob("COPYING*") + glob.glob("UNLICENSE*"):
+    lowered_name = os.path.splitext(license_file.lower())[0]
     if lowered_name == "license-apache":
       licenses.append(License(LicenseType.APACHE2, LicenseGroup.NOTICE, license_file))
     elif lowered_name == "license-mit":