Run tests for Ruby 3.1 and change from racer to mini_racer for Ruby 3.1 support

Gemfile.lock

@@ -157,7 +157,7 @@ GEM
       mime-types
       terrapin (~> 0.6.0)
     language_server-protocol (3.17.0.3)
-    libv8 (3.16.14.19)
+    libv8-node (21.7.2.0)
     listen (3.8.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
@@ -177,6 +177,8 @@ GEM
     mini_mime (1.1.5)
     mini_portile2 (2.8.5)
     minitest (5.23.1)
+    mini_racer (0.12.0)
+      libv8-node (~> 21.7.2.0)
     minitest-stub-const (0.6)
     mocha (2.1.0)
       ruby2_keywords (>= 0.0.5)
@@ -252,7 +254,6 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rbs (2.8.4)
-    ref (2.0.0)
     regexp_parser (2.8.3)
     reverse_markdown (2.1.1)
       nokogiri
@@ -326,9 +327,6 @@ GEM
       unicode-display_width (>= 1.1.1, < 3)
     terrapin (0.6.0)
       climate_control (>= 0.0.3, < 1.0)
-    therubyracer (0.12.3)
-      libv8 (~> 3.16.14.15)
-      ref
     thor (1.3.0)
     tilt (2.3.0)
     timeout (0.4.1)
@@ -375,6 +373,7 @@ DEPENDENCIES
   jquery-ui-rails (~> 6.0.1)
   kt-paperclip (~> 7.2)
   listen
+  mini_racer
   minitest-stub-const
   mocha
   mysql2 (~> 0.5.5)
@@ -393,7 +392,6 @@ DEPENDENCIES
   solargraph
   spring (~> 4)
   sqlite3
-  therubyracer
   tolk (~> 5.0.1)
   tracks-chartjs-ror
   uglifier (>= 1.3.0)