Fix Collection::implode() string argument (#41468)

collect(['foo', 'bar'])->implode('_') should be 'foo-bar' but it
instead attempts to call translator helper _().

For callable only support Closure, an invokable class, or a
[class, 'method'] array pair.

src/Illuminate/Collections/Collection.php

@@ -583,7 +583,7 @@ public function hasAny($key)
      */
     public function implode($value, $glue = null)
     {
-        if (is_callable($value)) {
+        if ($this->useAsCallable($value)) {
             return implode($glue ?? '', $this->map($value)->all());
         }
 

tests/Support/SupportCollectionTest.php

@@ -2151,6 +2151,7 @@ public function testImplode($collection)
         $data = new $collection([Str::of('taylor'), Str::of('dayle')]);
         $this->assertSame('taylordayle', $data->implode(''));
         $this->assertSame('taylor,dayle', $data->implode(','));
+        $this->assertSame('taylor_dayle', $data->implode('_'));
 
         $data = new $collection([['name' => 'taylor', 'email' => 'foo'], ['name' => 'dayle', 'email' => 'bar']]);
         $this->assertSame('taylor-foodayle-bar', $data->implode(fn ($user) => $user['name'].'-'.$user['email']));