ci: Enable GLES3 testing on db410c/db820c (freedreno a306 and a530).

We haven't had it enabled due tointermittent failures.  Those failures
are, as far as I can tell, due to GPU faults from buffer overflows where a
failing test in a thread stomps an otherwise passing thread's buffers.  By
running deqp single-threaded, we can get more consistent failures, at the
cost of needing to do a tiny subset of the tests to keep runtime down.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4685>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 6c6ff6a..0824670 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -821,10 +821,11 @@
 arm64_a306_gles3:
   extends:
     - arm64_a306_gles2
-    - .test-manual
-  parallel: 8
   variables:
     DEQP_VER: gles3
+    DEQP_PARALLEL: 1
+    CI_NODE_INDEX: 1
+    CI_NODE_TOTAL: 50
 
 arm64_a530_gles2:
   extends:
@@ -841,10 +842,11 @@
 arm64_a530_gles3:
   extends:
     - arm64_a530_gles2
-    - .test-manual
-  parallel: 6
   variables:
     DEQP_VER: gles3
+    DEQP_PARALLEL: 1
+    CI_NODE_INDEX: 1
+    CI_NODE_TOTAL: 100
 
 # RADV CI
 .test-radv: