Refactor update job to construct release body directly in environment variable and simplify body handling

.gitea/workflows/update.yaml

@@ -40,11 +40,19 @@ jobs:
           echo "DRAFT=$draft"           >>"$GITHUB_ENV"
           echo "PRERELEASE=$prerelease" >>"$GITHUB_ENV"
 
-           {
-            echo "BODY<<EOF"
-            printf '%s\n' "$body_text"
-            echo "EOF"
-          } >>"$GITHUB_ENV"
+          read -r -d '' RELEASE_BODY <<EOF
+          # Homebrewery $name Image
+
+          > _This is an automated Docker Image update. Nothing other than the Homebrewery version changed._
+
+          $body_text
+
+          See original Changelog from [$name]($url)
+          EOF
+          
+          echo "RELEASE_BODY<<EOF"      >>"$GITHUB_ENV"
+          printf '%s\n' "$RELEASE_BODY" >>"$GITHUB_ENV"
+          echo "EOF"                    >>"$GITHUB_ENV"
 
       - name: Debug step
         run: |
@@ -62,11 +70,4 @@ jobs:
           prerelease: ${{ env.PRERELEASE }}
           name: ${{ env.NAME }}
           tag_name: ${{ env.TAG_NAME }}
-          body: |
-            # Homebrewery ${{ env.$NAME }} Image
-
-            > _This is an automated Docker Image update. Nothing other than the Homebrewery version changed._
-
-            ${{ env.BODY }}
-
-            See original Changelog from [${{ env.NAME }}](${{ env.URL }})
+          body: ${{ env.RELEASE_BODY }}