Bug 1699886 - set background-color-transition-with-initially-transparent.html as intermittent on Linux debug.

Test got added in bug 1699671 / wpt PR 27907.

testing/web-platform/meta/css/css-backgrounds/animations/background-color-transition-with-initially-transparent.html.ini

@@ -4,6 +4,7 @@
     if not debug and (os == "win") and not webrender and (processor == "x86_64"): ["FAIL", "PASS"]
     if not debug and (os == "linux") and not fission: ["PASS", "FAIL"]
     if not debug and (os == "linux") and fission: ["FAIL", "PASS"]
+    if debug and (os == "linux") and not webrender and (processor == "x86_64"): ["FAIL", "PASS"]
     if not debug and (os == "android") and not webrender: ["PASS", "FAIL"]
     if not debug and (os == "android") and webrender: ["PASS", "FAIL"]
     if debug and (os == "android") and not webrender: ["PASS", "FAIL"]