fix(gatsby): null check for context

[tcoopman]

Description

I've ran into a case where context was undefined resulting in:

TypeError: Cannot read properties of undefined (reading 'telemetryResolverTimings')",
          "    at wrappedTracingResolver (/home/thomas/Workspace/aardling/2022.dddeurope.com/node_modules/gatsby/src/schema/resolvers.ts:679:17)",

there was a check on if (context?.tracer) already but not on the telemtryResolverTimings

Documentation

No updates need

[LekoArts]

Can you push an empty commit? For some reason the CI didn't trigger a run

[tcoopman]

it doesn't look like the windows_unit_tests failing has anything to do with this PR?

[LekoArts]

Thanks!