fix: check out branch before performing diff

Author: ARR4N

.github/workflows/diff_from_libevm-base.sh

@@ -2,6 +2,7 @@
 
 set -u;
 
+git checkout "${1}";
 git diff --diff-filter=a --word-diff --unified=0 libevm-base.."${1}" \
     ':(exclude).golangci.yml' \
-    ':(exclude).github/**'
+    ':(exclude).github/**';

.github/workflows/libevm-delta.yml

@@ -18,6 +18,6 @@ jobs:
       - name: Diff libevm-base..libevm
         run: |
           .github/workflows/diff_from_libevm-base.sh libevm
-      - name: Diff libevm-base..HEAD
+      - name: Diff libevm-base..${{ github.sha }}
         run: |
-          .github/workflows/diff_from_libevm-base.sh HEAD
+          .github/workflows/diff_from_libevm-base.sh ${{ github.sha }}