Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/7e15d7e2a38e
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #28989 from gaye/gaia-marionette-retry-hotfix-0-test-files

Hotfix for case when gaia_marionette_retry.js receives 0 test files

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https://hg.mozilla.org/integration/gaia-central/rev/5b91b8bdc6ca
Author: gaye <gaye@mozilla.com>
Desc: Hotfix for case when gaia_marionette_retry.js receives 0 test files

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "76f850a9b940117e59e14d353f72ce79c9fbf379", 
+        "git_revision": "b63fc09ee549fbaa5064517f44ef77f0754a11e8", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "03ddf0e1fdce3902230da23e0707071926d210b8", 
+    "revision": "7e15d7e2a38e4dcc6148c6fd0f5d34a5885feff6", 
     "repo_path": "integration/gaia-central"
 }