Fix doxygen text for cudf::dictionary::encode

[davidwendt]

Description

Fixes the example code in the doxygen comment for cudf::dictionary::encode to use the correct API name.
No function has change -- just code comments that generate public doxygen content.
https://docs.rapids.ai/api/libcudf/stable/group__dictionary__encode.html#ga06997026d694784d613f4590563a8b33

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov]

Codecov Report

Base: 87.40% // Head: 88.15% // Increases project coverage by +0.74% 🎉

Coverage data is based on head (7aeee19) compared to base (f72c4ce).
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #11991      +/-   ##
================================================
+ Coverage         87.40%   88.15%   +0.74%     
================================================
  Files               133      133              
  Lines             21833    21995     +162     
================================================
+ Hits              19084    19389     +305     
+ Misses             2749     2606     -143     

Impacted Files	Coverage Δ
python/strings_udf/strings_udf/__init__.py	86.27% <0.00%> (-10.61%)	⬇️
python/cudf/cudf/io/text.py	91.66% <0.00%> (-8.34%)	⬇️
python/cudf/cudf/core/_base_index.py	82.20% <0.00%> (-3.35%)	⬇️
python/strings_udf/strings_udf/_typing.py	94.73% <0.00%> (-1.06%)	⬇️
python/cudf/cudf/testing/dataset_generator.py	72.83% <0.00%> (-0.42%)	⬇️
python/dask_cudf/dask_cudf/backends.py	84.90% <0.00%> (-0.37%)	⬇️
python/dask_cudf/dask_cudf/core.py	73.92% <0.00%> (-0.21%)	⬇️
python/cudf/cudf/io/orc.py	92.94% <0.00%> (-0.09%)	⬇️
python/cudf/cudf/__init__.py	90.69% <0.00%> (ø)
python/cudf/cudf/utils/ioutils.py	79.47% <0.00%> (ø)
... and 22 more

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[davidwendt]

@gpucibot merge