Update conformance testing to yesterday's 0.0.9 release.

In that release we ended up removing the `supports-trusted-root`
option from the conformance test Action.

Signed-off-by: Zach Steindler <steiza@github.com>

.github/workflows/conformance.yml

@@ -39,8 +39,7 @@ jobs:
 
       - run: go build -o conformance cmd/conformance/main.go
 
-      - uses: sigstore/sigstore-conformance@main # maybe we should pin this in the future, once sigstore-conformance development slows down?
+      - uses: sigstore/sigstore-conformance@c8d17eb7ee884cf86b93a3a3f471648fb0a83819 # v0.0.9
         with:
           entrypoint: ${{ github.workspace }}/conformance
           skip-signing: true
-          supports-trusted-root: true