ci/turnip: Drop two 660 vk jobs and tune down the vk coverage fraction.

We want another runner so we can do trace replay pre-merge.  And the vk
job was pushing our time targets, and oversubscribed by a board, so we
have to drop a bunch of coverage.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40959>

src/freedreno/ci/deqp-freedreno-a660-vk.toml

@@ -3,7 +3,7 @@
 deqp = "/deqp-vk/external/vulkancts/modules/vulkan/deqp-vk"
 caselists = ["/deqp-vk/mustpass/vk-main.txt"]
 renderer_check = "Turnip Adreno .* 660"
-fraction = 3
+fraction = 6
 tests_per_group = 10000
 [deqp.env]
 # Enable additional tests that test fp32 denorm preserve.

src/freedreno/ci/gitlab-ci.yml

@@ -277,7 +277,7 @@ a660-vk:
     - .lava-arm64-test-vk
     - .collabora-turnip-rules
     - .lava-sm8350-hdk:arm64
-  parallel: 5
+  parallel: 3
   variables:
     DEQP_SUITE: freedreno-a660-vk
     FLAKES_CHANNEL: "#freedreno-ci"