fix file extension (microsoft#35825)

Author: a-tarasyuk

src/testRunner/unittests/config/showConfig.ts

@@ -37,7 +37,7 @@ namespace ts {
 
         showTSConfigCorrectly("Default initialized TSConfig", ["--showConfig"]);
 
-        showTSConfigCorrectly("Show TSConfig with files options", ["--showConfig", "file0.st", "file1.ts", "file2.ts"]);
+        showTSConfigCorrectly("Show TSConfig with files options", ["--showConfig", "file0.ts", "file1.ts", "file2.ts"]);
 
         showTSConfigCorrectly("Show TSConfig with boolean value compiler options", ["--showConfig", "--noUnusedLocals"]);
 

tests/baselines/reference/showConfig/Show TSConfig with files options/tsconfig.json

@@ -1,7 +1,7 @@
 {
     "compilerOptions": {},
     "files": [
-        "./file0.st",
+        "./file0.ts",
         "./file1.ts",
         "./file2.ts"
     ]