Bump apollo-server-core from 2.21.0 to 2.26.2

Bumps [apollo-server-core](https://github.com/apollographql/apollo-server/tree/HEAD/packages/apollo-server-core) from 2.21.0 to 2.26.2.
- [Release notes](https://github.com/apollographql/apollo-server/releases)
- [Commits](https://github.com/apollographql/apollo-server/commits/[email protected]/packages/apollo-server-core)

---
updated-dependencies:
- dependency-name: apollo-server-core
  dependency-type: indirect
...

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