CI: pass secrets on to sign.yml so it can read the environment's key

.github/workflows/build.yml

@@ -508,3 +508,5 @@ jobs:
     with:
       environment: ${{ github.ref == 'refs/heads/main' && 'signing-main' || 'signing-branch' }}
       variants: '["standard"]'
+    # The key is an environment secret; a called workflow sees secrets only when they are passed on.
+    secrets: inherit

.github/workflows/release.yml

@@ -64,3 +64,5 @@ jobs:
       run_id: ${{ needs.find.outputs.run_id }}
       label: ${{ inputs.version }}
       artifact: droiddeck-release
+    # The key is an environment secret; a called workflow sees secrets only when they are passed on.
+    secrets: inherit