Rebuild docs only if source files change

[dgzlopes]

This PR uses on.push.paths workflow syntax, so we don't have to rebuild the docs unless source files have changed (based on #167 from @c24t).

I think that this path-based approach triggers less unnecessary than a file-based one.

I asked for feedback on Gitter, and I would love if someone had time to throw some thoughts on this :)

Signed-off-by: Daniel González Lopes danielgonzalezlopes@gmail.com

[codecov-io]

Codecov Report

Merging #380 into master will increase coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #380      +/-   ##
==========================================
+ Coverage   85.08%   85.22%   +0.14%     
==========================================
  Files          38       38              
  Lines        1897     1916      +19     
  Branches      225      226       +1     
==========================================
+ Hits         1614     1633      +19     
  Misses        218      218              
  Partials       65       65

Impacted Files	Coverage Δ
...app/src/opentelemetry_example_app/flask_example.py	100% <0%> (ø)	⬆️
...emetry-sdk/src/opentelemetry/sdk/trace/__init__.py	90.94% <0%> (+0.06%)	⬆️
...src/opentelemetry/ext/opentracing_shim/__init__.py	95.93% <0%> (+0.17%)	⬆️
...xt-jaeger/src/opentelemetry/ext/jaeger/__init__.py	85.18% <0%> (+0.18%)	⬆️
...ts/src/opentelemetry/ext/http_requests/__init__.py	89.74% <0%> (+0.26%)	⬆️
opentelemetry-sdk/src/opentelemetry/sdk/util.py	85.88% <0%> (+0.34%)	⬆️
...opentelemetry/sdk/context/propagation/b3_format.py	87.27% <0%> (+0.48%)	⬆️
...ry-ext-wsgi/src/opentelemetry/ext/wsgi/__init__.py	68.18% <0%> (+0.58%)	⬆️
...ry-sdk/src/opentelemetry/sdk/resources/__init__.py	70.83% <0%> (+2.65%)	⬆️

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[c24t]

Nice! This looks like a clear improvement to me.

[codeboten]

Makes sense to me