CI: Disable Panfrost Mali-T820, Lima Mali-400 and Lima Mali-450 jobs

The runners appear to be unhealthy.  Disable for now so people can merge
patches for other drivers in the meantime.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5619>

.gitlab-ci/lava-gitlab-ci.yml

@@ -137,7 +137,7 @@ panfrost-t860-gles3:arm64:
   tags:
     - mesa-ci-aarch64-lava-collabora
 
-panfrost-t820-gles2:arm64:
+.panfrost-t820-gles2:arm64:
   extends:
     - .lava-test:arm64
     - .panfrost-rules
@@ -149,7 +149,7 @@ panfrost-t820-gles2:arm64:
   tags:
     - mesa-ci-aarch64-lava-baylibre
 
-lima-mali400-test:armhf:
+.lima-mali400-test:armhf:
   parallel: 2
   extends:
     - .lava-test:armhf
@@ -161,7 +161,7 @@ lima-mali400-test:armhf:
   tags:
     - mesa-ci-aarch64-lava-baylibre
 
-lima-mali450-test:arm64:
+.lima-mali450-test:arm64:
   extends:
     - .lava-test:arm64
     - .lima-rules