Fix bridge/opencensus NewMetricExporter deprecation notice

[MrAlias]

NewMetricExporter in go.opentelemetry.io/otel/bridge/opencensus was deprecated in v0.35.0 (#3541). However, the notice did not have a preceding blank line in the documentation. Because of this, the documentation for this package does not correctly render the notice:

These changes fix that formatting resulting in the following when rendered locally:

expanded:

This will also trigger linters about the deprecation notice.

[codecov]

Codecov Report

Merging #4470 (517b667) into main (e528731) will increase coverage by 0.0%.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main   #4470   +/-   ##
=====================================
  Coverage   81.3%   81.3%           
=====================================
  Files        220     220           
  Lines      17662   17662           
=====================================
+ Hits       14370   14372    +2     
+ Misses      2992    2990    -2     
  Partials     300     300           

Files Changed	Coverage
bridge/opencensus/metric.go	ø

[dashpole]

TIL