Fix update of node-fetch for vulnerability (SCP-4029)

[eweitz]

This fixes a security vulnerability in node-fetch in a way that doesn't break SCP automated tests.

Dependabot bumped node-fetch up a major version to fix a vulnerability (#1326). The test failed with a false positive as noted there, but a true positive failure also occurred, went unnoticed, and now consistently breaks CI. The true-positive was caused by breaking changes in the major node-fetch update.

Further research indicates the vulnerability can be fixed by a minor node-fetch update, to version 2.6.7. This change does that. Local testing indicates it works.

To test:

• Pull
• yarn install
• yarn test
• Confirm tests pass

This satisfies SCP-4029.