CI: move clipboard tests to an allowed-failure test

[jreback]

CI: change 2.7-build_test -> 3.6-build_test

[codecov]

Codecov Report

Merging #18251 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18251      +/-   ##
==========================================
- Coverage   91.43%   91.41%   -0.02%     
==========================================
  Files         164      164              
  Lines       50090    50090              
==========================================
- Hits        45798    45789       -9     
- Misses       4292     4301       +9

Flag	Coverage Δ
#multiple	89.22% <ø> (ø)	⬆️
#single	39.52% <ø> (-0.92%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/io/clipboard/clipboards.py	24.05% <0%> (-2.54%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️
pandas/core/indexes/datetimes.py	95.48% <0%> (+0.09%)	⬆️
pandas/io/clipboard/__init__.py	76.19% <0%> (+2.38%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9e3ad63...35cafbd. Read the comment docs.

[codecov]

Codecov Report

Merging #18251 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18251      +/-   ##
==========================================
- Coverage   91.43%   91.39%   -0.05%     
==========================================
  Files         164      164              
  Lines       50090    50096       +6     
==========================================
- Hits        45798    45783      -15     
- Misses       4292     4313      +21

Flag	Coverage Δ
#multiple	89.2% <ø> (-0.02%)	⬇️
#single	39.52% <ø> (-0.92%)	⬇️

Impacted Files	Coverage Δ
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/io/clipboard/clipboards.py	24.05% <0%> (-2.54%)	⬇️
pandas/plotting/_converter.py	63.38% <0%> (-1.82%)	⬇️
pandas/core/frame.py	97.8% <0%> (-0.1%)	⬇️
pandas/core/groupby.py	92.03% <0%> (ø)	⬆️
pandas/io/sas/sas7bdat.py	91.07% <0%> (+0.01%)	⬆️
pandas/core/computation/eval.py	97.11% <0%> (+0.08%)	⬆️
pandas/core/indexes/datetimes.py	95.48% <0%> (+0.09%)	⬆️
pandas/io/clipboard/__init__.py	76.19% <0%> (+2.38%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9e3ad63...35cafbd. Read the comment docs.