Declare dependency on bcmath extension

These tests fail if the 'bcmath' PHP extension is not loaded. Elsewhere, we use
this syntax to skip tests which depend on the 'bcmath' extension.

Author: fredden

tests/Core/Ruleset/ProcessRulesetShouldProcessElementTest.php

@@ -209,6 +209,8 @@ public function testShouldProcessArgCbfonly()
      * Verify that in CS mode, phpcs-only <ini> directives are respected and phpcbf-only <ini>
      * directives are ignored.
      *
+     * @requires extension bcmath
+     *
      * @return void
      */
     public function testShouldProcessIniCsonly()
@@ -229,6 +231,7 @@ public function testShouldProcessIniCsonly()
      * directives are ignored.
      *
      * @group CBF
+     * @requires extension bcmath
      *
      * @return void
      */