PHP 7.4RC4, pdo_* extensions and test workflow.

[shivammathur]

• Switch to PHP7.4RC4 on windows and macOS
• Add support for extensions with pdo prefix like pdo_mysql and pdo_sqlite. Fixes pdo_mysql and pdo_sqlite should install when specified in extension-csv input #61
• Fix test workflow to timeout codecov command

[codecov]

Codecov Report

Merging #62 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master    #62   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           4      4           
  Lines         204    204           
=====================================
  Hits          204    204

Impacted Files	Coverage Δ
src/utils.ts	100% <ø> (ø)	⬆️

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