[C++] Use GTEST_SKIP in parquet encoding tests

[asfimport]

As per a TODO left in ARROW-3769 / #3721 we can now use the GTEST_SKIP macro in parquet/encoding-test.cpp. GTEST_SKIP was added in gtest 1.10.0 so this involves bumping our minimal gtest version from 1.8.1

Reporter: Andrew Wieteska / @arw2019
Assignee: Andrew Wieteska / @arw2019

PRs and other links:

• GitHub Pull Request #8782

_{Note: This issue was originally created as ARROW-10746. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
+1. We can also use it elsewhere.

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 8782
#8782