Update taiki-e/install-action digest to 6608b29

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@672949f0e99e12c1a48510fa548e812f6835397f # v2
+        uses: taiki-e/install-action@6608b29f1fd1773aafb923cffd26c3a528f72083 # v2
         with:
           tool: cargo-readme
       - name: Run cargo readme