Fix links to Google test

[vyasr]

This PR fixes some broken links in the developer testing guide.

[vyasr]

@gpucibot merge

[codecov]

Codecov Report

Merging #7958 (31250d7) into branch-0.20 (599f62d) will increase coverage by 0.02%.
The diff coverage is 92.68%.

❗ Current head 31250d7 differs from pull request most recent head 498ebf6. Consider uploading reports for the commit 498ebf6 to get more accurate results

@@               Coverage Diff               @@
##           branch-0.20    #7958      +/-   ##
===============================================
+ Coverage        82.30%   82.32%   +0.02%     
===============================================
  Files              101      103       +2     
  Lines            17053    17347     +294     
===============================================
+ Hits             14035    14281     +246     
- Misses            3018     3066      +48     

Impacted Files	Coverage Δ
python/cudf/cudf/utils/dtypes.py	83.44% <ø> (-6.45%)	⬇️
python/cudf/cudf/utils/utils.py	82.85% <ø> (-2.21%)	⬇️
python/cudf/cudf/core/groupby/groupby.py	92.25% <78.57%> (-1.21%)	⬇️
python/cudf/cudf/core/column/lists.py	86.95% <80.00%> (-0.27%)	⬇️
python/cudf/cudf/core/column/struct.py	96.15% <86.66%> (-3.85%)	⬇️
python/cudf/cudf/core/index.py	92.58% <88.09%> (-0.44%)	⬇️
python/cudf/cudf/core/column/column.py	87.77% <88.57%> (+0.33%)	⬆️
python/cudf/cudf/core/column/decimal.py	92.92% <91.48%> (-0.92%)	⬇️
python/cudf/cudf/core/column/interval.py	90.69% <92.30%> (+0.07%)	⬆️
python/cudf/cudf/core/join/join.py	96.72% <93.75%> (+0.20%)	⬆️
... and 25 more

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