test_runner: pass FORCE_COLOR to child process

PR-URL: nodejs#48057
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Antoine du Hamel <[email protected]>

Author: MoLow

test/fixtures/test-runner/output/arbitrary-output-colored.snapshot

@@ -1,5 +1,7 @@
 { foo: [32m'bar'[39m }
+
 [33m1[39m
+
 [32m✔ passing test [90m(*ms)[39m[39m
 [34mℹ tests 1[39m
 [34mℹ suites 0[39m
@@ -11,7 +13,9 @@
 [34mℹ duration_ms *[39m
 TAP version 13
 # { foo: [32m'bar'[39m }
+# 
 # [33m1[39m
+# 
 # Subtest: passing test
 ok 1 - passing test
   ---