Bump actions/cache from 2 to 3

Bumps [actions/cache](https://github.com/actions/cache) from 2 to 3.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2...v3)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -211,7 +211,7 @@ jobs:
           profile: minimal
       - name: Cache routing graph snapshot
         id: cache-graph
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: lightning/net_graph-2021-05-31.bin
           key: ldk-net_graph-v0.0.15-2021-05-31.bin