Bug 1622072 [wpt PR 22226] - correct default expectation for existing…

… mrow test, a=testonly

Automatic update from web-platform-tests
correct default expectation for existing mrow test (#22226)

* Update tabindex-001.html

Attempting to match defaults defined in whatwg/html#5248
definitely needs scrutiny..

* Update tabindex-001.html

The default `.tabIndex` of an mrow should be 0 regardless of when it has an href or not, as a linkable element and matching historical (oddity) of other linkable things in HTML/SVG
--

wpt-commits: 6b2fee71a825487369f34f82e7daa732920d186e
wpt-pr: 22226

UltraBlame original commit: 88b6c5710ce466879d3991f983b9d5397d60a222

testing/web-platform/tests/mathml/relations/html5-tree/tabindex-001.html

@@ -191,8 +191,7 @@
 mrow
 .
 tabIndex
--
-1
+0
 "
 no
 attribute
@@ -231,8 +230,7 @@
 mrow
 .
 tabIndex
--
-1
+0
 "
 invalid
 "
@@ -270,8 +268,7 @@
 mrow
 .
 tabIndex
--
-1
+0
 "
 too
 large