chore: fixing parent span for graphql

[obecny]

Which problem is this PR solving?

• Fixes Many graphql.execute spans have the same parent span id #294

Short description of the changes

• Fixes the parent span for main spans

[codecov]

Codecov Report

Merging #299 (915b5bb) into master (e3de6ba) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #299   +/-   ##
=======================================
  Coverage   95.33%   95.33%           
=======================================
  Files         115      115           
  Lines        5998     5965   -33     
  Branches      592      588    -4     
=======================================
- Hits         5718     5687   -31     
+ Misses        280      278    -2     

Impacted Files	Coverage Δ
...entelemetry-instrumentation-graphql/src/symbols.ts	100.00% <ø> (ø)
...entelemetry-instrumentation-graphql/src/graphql.ts	92.14% <100.00%> (+0.75%)	⬆️
...opentelemetry-instrumentation-graphql/src/types.ts	100.00% <100.00%> (ø)
...metry-instrumentation-graphql/test/graphql.test.ts	100.00% <100.00%> (ø)

[chrisdostert]

Awesome contribution; i've been seeing this as well. Is it possible to get a release cut?