Fix compile error with GCC 11.3

[tyler92]

Fixes #2026

Changes

There was a compile error with GCC 11.3 and the following cmake options:

-DBUILD_TESTING=OFF -DWITH_EXAMPLES_HTTP=ON -DWITH_PROMETHEUS=ON -DWITH_STL=ON

GCC output:

In file included from opentelemetry-cpp/examples/http/client.cc:7:
opentelemetry-cpp/examples/http/tracer_common.h:29:26: error: expected ‘)’ before ‘&’ token
   29 |   HttpTextMapCarrier<T>(T &headers) : headers_(headers) {}

See https://godbolt.org/z/Pv3fqq7zx

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: tyler92 (e36415d)

[codecov]

Codecov Report

Merging #2025 (6698434) into main (2b08db2) will increase coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2025      +/-   ##
==========================================
+ Coverage   87.30%   87.32%   +0.03%     
==========================================
  Files         166      166              
  Lines        4723     4723              
==========================================
+ Hits         4123     4124       +1     
+ Misses        600      599       -1     

Impacted Files	Coverage Δ
sdk/src/trace/batch_span_processor.cc	91.48% <0.00%> (+0.78%)	⬆️

[marcalff]

LGTM, thanks for the fix.

[owent]

LGTM and thanks.