Reenable the nexus 6p tests (#136689)

*Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.*

*List which issues are fixed by this PR. You must list at least one issue.*

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

.ci.yaml

@@ -458,6 +458,7 @@ targets:
           "--device", "model=Nexus5,version=22",
           "--device", "model=Nexus5,version=23",
           "--device", "model=Nexus5,version=24",
+          "--device", "model=Nexus6P,version=25",
           "--device", "model=Nexus6P,version=26",
           "--device", "model=Nexus6P,version=27"
         ]
@@ -488,6 +489,7 @@ targets:
           "--device", "model=Nexus5,version=21",
           "--device", "model=Nexus5,version=22",
           "--device", "model=Nexus5,version=23",
+          "--device", "model=Nexus6P,version=25",
           "--device", "model=Nexus6P,version=26",
           "--device", "model=Nexus6P,version=27"
         ]
@@ -518,6 +520,7 @@ targets:
           "--device", "model=Nexus5,version=21",
           "--device", "model=Nexus5,version=22",
           "--device", "model=Nexus5,version=23",
+          "--device", "model=Nexus6P,version=25",
           "--device", "model=Nexus6P,version=26",
           "--device", "model=Nexus6P,version=27"
         ]