fix release.yaml (#34)

Signed-off-by: hantmac <hantmac@outlook.com>

.github/workflows/release.yaml

@@ -71,8 +71,6 @@ jobs:
     runs-on: ubuntu-latest
     name: upload-sha256sums
     steps:
-      - name: Checkout
-        uses: actions/checkout@v2
       - name: Get release
         id: get_release
         uses: bruceadams/get-release@v1.2.2
@@ -82,7 +80,7 @@ jobs:
           name: sha256sums
       - shell: bash
         run: |
-          for file in *
+          for file in *.txt
           do
             cat ${file} >> sha256sums.txt
           done