tests: skip ugoira tests if ffmpeg/mkvmerge not installed.

Gemfile.lock

@@ -152,8 +152,6 @@ GEM
     ffaker (2.12.0)
     ffi (1.11.1)
     ffi (1.11.1-x64-mingw32)
-    ffi-win32-extensions (1.0.3)
-      ffi
     flamegraph (0.9.5)
     get_process_mem (0.2.4)
       ffi (~> 1.0)
@@ -290,9 +288,6 @@ GEM
       unicode (~> 0.4.4)
     pry-rails (0.3.9)
       pry (>= 0.10.4)
-    ptools (1.3.5)
-    ptools (1.3.5-universal-mingw32)
-      win32-file (>= 0.7.0)
     public_suffix (3.1.1)
     rack (2.0.7)
     rack-contrib (2.1.0)
@@ -440,14 +435,6 @@ GEM
     websocket-extensions (0.1.4)
     whenever (1.0.0)
       chronic (>= 0.6.3)
-    win32-file (0.8.2)
-      ffi
-      ffi-win32-extensions
-      win32-file-stat (>= 1.4.0)
-    win32-file-stat (1.5.5)
-      ffi
-      ffi-win32-extensions
-    win32console (1.3.2)
     zeitwerk (2.1.9)
 
 PLATFORMS
@@ -496,7 +483,6 @@ DEPENDENCIES
   pry-byebug
   pry-inline
   pry-rails
-  ptools
   rack-mini-profiler
   rails (~> 6.0)
   rakismet