Bump pghero from 2.7.4 to 2.8.0 (#15907)

Bumps [pghero](https://github.com/ankane/pghero) from 2.7.4 to 2.8.0.
- [Release notes](https://github.com/ankane/pghero/releases)
- [Changelog](https://github.com/ankane/pghero/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ankane/pghero/compare/v2.7.4...v2.8.0)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -411,7 +411,7 @@ GEM
     pastel (0.8.0)
       tty-color (~> 0.5)
     pg (1.2.3)
-    pghero (2.7.4)
+    pghero (2.8.0)
       activerecord (>= 5)
     pkg-config (1.4.5)
     pluck_each (0.1.3)
@@ -770,7 +770,7 @@ DEPENDENCIES
   parallel_tests (~> 3.5)
   parslet
   pg (~> 1.2)
-  pghero (~> 2.7)
+  pghero (~> 2.8)
   pkg-config (~> 1.4)
   pluck_each (~> 0.1.3)
   posix-spawn