refactor(animations): do not assign to innerHTML (#37397)

This should not change behavior, but it prevents false-positive warnings in various static analysis
tools, including tools used internally at Google.

PR Close #37397

packages/animations/browser/src/render/css_keyframes/css_keyframes_driver.ts

@@ -72,7 +72,7 @@ export class CssKeyframesDriver implements AnimationDriver {
     keyframeStr += `}\n`;
 
     const kfElm = document.createElement('style');
-    kfElm.innerHTML = keyframeStr;
+    kfElm.textContent = keyframeStr;
     return kfElm;
   }