ci: run tests with no treesitter parsers installed

.github/workflows/ci.yml

@@ -167,11 +167,12 @@ jobs:
             runner: macos-11.0
             os: osx
 
-            # The functionaltest-lua test two things simultaneously:
+            # functionaltest-lua is our dumping ground for non-mainline configurations.
             # 1. Check that the tests pass with PUC Lua instead of LuaJIT.
             # 2. Use as oldest/minimum versions of dependencies/build tools we
             #    still explicitly support so we don't accidentally rely on
             #    features that is only available on later versions.
+            # 3. No treesitter parsers installed.
           - flavor: functionaltest-lua
             cc: gcc
             runner: ubuntu-20.04

.github/workflows/env.sh

@@ -64,7 +64,7 @@ EOF
   functionaltest-lua)
     BUILD_FLAGS="$BUILD_FLAGS -DPREFER_LUA=ON"
     FUNCTIONALTEST=functionaltest-lua
-    DEPS_CMAKE_FLAGS="$DEPS_CMAKE_FLAGS -DUSE_BUNDLED_LUAJIT=OFF"
+    DEPS_CMAKE_FLAGS="$DEPS_CMAKE_FLAGS -DUSE_BUNDLED_LUAJIT=OFF -DUSE_BUNDLED_TS_PARSERS=OFF"
     ;;
   *)
     ;;