Update GHA and Drone

[sdarwin]

• gcc 11
• clang 12
• msvc 14.3

note: CXXSTD 14 and 17 are timing out on msvc 14.3. CXXSTD 20 is successful.

[cppalliance-bot]

An automated preview of the documentation is available at https://2351.beastdocs.prtest.cppalliance.org/libs/beast/doc/html/index.html

[codecov]

Codecov Report

Merging #2351 (96e58d3) into develop (94e6f14) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #2351   +/-   ##
========================================
  Coverage    94.86%   94.86%           
========================================
  Files          151      151           
  Lines        12228    12228           
========================================
  Hits         11600    11600           
  Misses         628      628           

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