CI: ensure prebuilds use Node API version 7

Author: lovell

.github/workflows/ci-darwin-arm64v8.yml

@@ -33,4 +33,4 @@ jobs:
         if: matrix.prebuild && startsWith(github.ref, 'refs/tags/')
         env:
           prebuild_upload: ${{ secrets.GITHUB_TOKEN }}
-        run: npx prebuild --runtime napi --target 5
+        run: npx prebuild --runtime napi --target 7

.github/workflows/ci.yml

@@ -99,4 +99,4 @@ jobs:
         if: matrix.prebuild && startsWith(github.ref, 'refs/tags/')
         env:
           prebuild_upload: ${{ secrets.GITHUB_TOKEN }}
-        run: npx prebuild --runtime napi --target 5
+        run: npx prebuild --runtime napi --target 7