Explicitly use the <string> header in crashinfo.cpp

[danielsn]

What does this PR do?

Explicitly uses <string> as a header for crashinfo.cpp.

Motivation

Windows CI was failing. https://github.com/DataDog/libdatadog/actions/runs/9402609405/job/25900083549 This looked like it might fix the error

Additional Notes

Anything else we should know when reviewing?

How to test the change?

Describe here in detail how the change can be validated.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.24%. Comparing base (bcc567a) to head (fd2e507).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #472   +/-   ##
=======================================
  Coverage   69.24%   69.24%           
=======================================
  Files         195      195           
  Lines       26051    26051           
=======================================
  Hits        18039    18039           
  Misses       8012     8012           

Components	Coverage Δ
crashtracker	17.62% <ø> (ø)
datadog-alloc	98.76% <ø> (ø)
data-pipeline	51.45% <ø> (ø)
data-pipeline-ffi	0.00% <ø> (ø)
ddcommon	86.43% <ø> (ø)
ddcommon-ffi	74.15% <ø> (ø)
ddtelemetry	56.11% <ø> (ø)
ipc	84.53% <ø> (ø)
profiling	77.83% <ø> (ø)
profiling-ffi	59.61% <ø> (ø)
serverless	0.00% <ø> (ø)
sidecar	36.29% <ø> (ø)
sidecar-ffi	0.00% <ø> (ø)
spawn-worker	54.98% <ø> (ø)
trace-mini-agent	69.33% <ø> (ø)
trace-normalization	97.79% <ø> (ø)
trace-obfuscation	95.74% <ø> (ø)
trace-protobuf	33.33% <ø> (ø)
trace-utils	90.94% <ø> (ø)