Update shakapacker to latest from early-hints branch

Updated to commit 915edce51481bb1135853f9b877fd243623a9820 from
shakapacker's justin808/early-hints branch.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

Gemfile.lock

@@ -1,6 +1,6 @@
 GIT
   remote: https://github.com/shakacode/shakapacker.git
-  revision: 9a55db5d7c798154ecc2a95121ef3afa63f1e13e
+  revision: 915edce51481bb1135853f9b877fd243623a9820
   branch: justin808/early-hints
   specs:
     shakapacker (9.3.0.beta.2)

yarn.lock

@@ -9154,7 +9154,7 @@ [email protected]:
 
 "shakapacker@github:shakacode/shakapacker#justin808/early-hints":
   version "9.3.0-beta.2"
-  resolved "https://codeload.github.com/shakacode/shakapacker/tar.gz/9a55db5d7c798154ecc2a95121ef3afa63f1e13e"
+  resolved "https://codeload.github.com/shakacode/shakapacker/tar.gz/915edce51481bb1135853f9b877fd243623a9820"
   dependencies:
     js-yaml "^4.1.0"
     path-complete-extname "^1.0.0"