Bug 1868998 - Mark custom-car jobs as running nowhere and not being cached. r=taskgraph-reviewers,kshampur,jcristau

They are triggered via cron, so an empty run-on-projects should be the
appropriate config.

As they are not idempotent (they will pick the last from upstream on
each run), they also shouldn't be cached.

Differential Revision: https://phabricator.services.mozilla.com/D197303

taskcluster/ci/toolchain/misc.yml

@@ -201,10 +201,13 @@ macosx64-xz:
 macosx64-custom-car:
     description: "Custom chromium-as-release build for mac"
     worker-type: b-osx-1015
+    attributes:
+        cached_task: false
     treeherder:
         symbol: TM(custom-car)
     worker:
         max-run-time: 35000
+    run-on-projects: []
     run:
         script: build-custom-car.sh
         arguments: [
@@ -233,11 +236,14 @@ macosx64-custom-car:
 macosx-arm64-custom-car:
     description: "Custom chromium-as-release build for mac (apple silicon)"
     worker-type: b-osx-1015
+    attributes:
+        cached_task: false
     treeherder:
         symbol: TM(custom-car-arm)
         tier: 3
     worker:
         max-run-time: 50000
+    run-on-projects: []
     run:
         script: build-custom-car.sh
         arguments: [
@@ -265,11 +271,14 @@ macosx-arm64-custom-car:
 
 android-custom-car:
     description: "Custom chromium-as-release build for Android"
+    attributes:
+        cached_task: false
     treeherder:
         symbol: TL(custom-car-android)
     worker:
         docker-image: {in-tree: custom-car-android}
         max-run-time: 20000
+    run-on-projects: []
     run:
         script: build-custom-car.sh
         arguments: [
@@ -296,11 +305,14 @@ android-custom-car:
 
 linux64-custom-car:
     description: "Custom chromium-as-release build for Linux"
+    attributes:
+        cached_task: false
     treeherder:
         symbol: TL(custom-car)
     worker:
         docker-image: {in-tree: custom-car-linux}
         max-run-time: 16200
+    run-on-projects: []
     run:
         script: build-custom-car.sh
         arguments: [
@@ -324,6 +336,8 @@ linux64-custom-car:
 
 win64-custom-car:
     description: "Custom chromium-as-release build for Windows"
+    attributes:
+        cached_task: false
     treeherder:
         symbol: TW64(custom-car)
     worker-type: b-win2022
@@ -331,6 +345,7 @@ win64-custom-car:
         max-run-time: 16200
         env:
             MSYSTEM: "MINGW64"
+    run-on-projects: []
     run:
         script: build-custom-car.sh
         arguments: [