Correct format string in logging messages (#15363)

diff --git a/tools/wpt/browser.py b/tools/wpt/browser.py
index 5f711f4..c446980 100644
--- a/tools/wpt/browser.py
+++ b/tools/wpt/browser.py
@@ -469,7 +469,7 @@
                 return None
             m = re.match(r"Google Chrome (.*)", version_string)
             if not m:
-                self.logger.warning("Failed to extract version from: s%", version_string)
+                self.logger.warning("Failed to extract version from: %s", version_string)
                 return None
             return m.group(1)
         self.logger.warning("Unable to extract version from binary on Windows.")
@@ -667,7 +667,7 @@
             return None
         m = re.match(r"Included with Safari (.*)", version_string)
         if not m:
-            self.logger.warning("Failed to extract version from: s%", version_string)
+            self.logger.warning("Failed to extract version from: %s", version_string)
             return None
         return m.group(1)