[BUG] Panic from v1.66 on startup

[picollomartin]

Version of dd-trace-go
v.1.68.0

Describe what happened:
With an upgrade from version 1.58 to latest 1.68, tracer start to panic

We trace down the panic to this PR, because occurs here:

dd-trace-go/ddtrace/tracer/log.go

Lines 130 to 131 in 5b9a8af

	PropagationStyleInject: cp.injectorNames,
	PropagationStyleExtract: cp.extractorsNames,

Workaround is disable startup log (by env variable or in code)

Describe what you expected:
Not panic, instead if propagator is not the expected one ignore those fields

Steps to reproduce the issue:

• Override with some custom propagator using tracer.WithPropagator
• Start tracer with tracer.WithLogStartup(true) (enabled by default, you can skip this)
• Tracer panics when reach this lines

Additional environment details (Version of Go, Operating System, etc.):
Go 1.22 - linux

[mtoffl01]

Thanks for reporting this! We're working on a fix for it now.