fix context propagation for logs

[giortzisg]

Description

This PR fixes two issues with how the context was passed on logs:

• check for falling back on the initialization context, if slog is passing context.Background()
• use SpanFromContext first and then default back to GetHubFromContext.

Issues

• resolves: Slog integration only attaches to trace when using slog.***Context() #1117
• resolves: GO-92

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.89%. Comparing base (c982e6f) to head (1ad35f2).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
slog/sentryslog.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1118      +/-   ##
==========================================
+ Coverage   86.67%   86.89%   +0.22%     
==========================================
  Files          60       61       +1     
  Lines        6964     5557    -1407     
==========================================
- Hits         6036     4829    -1207     
+ Misses        743      542     -201     
- Partials      185      186       +1     

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[giortzisg]

StartSpan adds the span as a context key, so it doesn't matter where it originates from, it only matters if the key exists.

[lcian]

Should we add tests for the change?
Does any other logger need to be updated with this fix?

[linear]

GO-92 Slog integration only attaches to trace when using slog.***Context()

[lcian]

LGTM