Bump strong_migrations from 0.7.4 to 0.7.6 (#15581)

Bumps [strong_migrations](https://github.com/ankane/strong_migrations) from 0.7.4 to 0.7.6.
- [Release notes](https://github.com/ankane/strong_migrations/releases)
- [Changelog](https://github.com/ankane/strong_migrations/blob/master/CHANGELOG.md)
- [Commits](https://github.com/ankane/strong_migrations/compare/v0.7.4...v0.7.6)

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

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

Gemfile.lock

@@ -350,7 +350,7 @@ GEM
     mimemagic (0.3.5)
     mini_mime (1.0.2)
     mini_portile2 (2.5.0)
-    minitest (5.14.2)
+    minitest (5.14.3)
     msgpack (1.3.3)
     multi_json (1.15.0)
     multipart-post (2.1.1)
@@ -612,7 +612,7 @@ GEM
     stoplight (2.2.1)
     streamio-ffmpeg (3.0.2)
       multi_json (~> 1.8)
-    strong_migrations (0.7.4)
+    strong_migrations (0.7.6)
       activerecord (>= 5)
     temple (0.8.2)
     terminal-table (2.0.0)