Update taiki-e/install-action digest to 6f9c7cc (#386)

Author: nextest-bot

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Lint (rustfmt)
         run: cargo xfmt --check
       - name: Install cargo readme
-        uses: taiki-e/install-action@f535147c22906d77695e11cb199e764aa610a4fc # v2
+        uses: taiki-e/install-action@6f9c7cc51aa54b13cbcbd12f8bbf69d8ba405b4b # v2
         with:
           tool: cargo-readme
       - name: Run cargo readme