Use pre to run 1.12 pre-release in tests

Author: Viral Shah

.buildkite/runtests.yml

@@ -13,7 +13,7 @@ steps:
           gid: 1000
       # Julia installation inside the sandbox
       - JuliaCI/julia#v1:
-          version: "nightly"
+          version: "pre"
           arch: "i686"
     command: |
       julia --color=yes --code-coverage=@ .ci/run_tests.jl
@@ -37,7 +37,7 @@ steps:
           gid: 1000
       # Julia installation inside the sandbox
       - JuliaCI/julia#v1:
-          version: "nightly"
+          version: "pre"
     command: |
       julia --color=yes --code-coverage=@ .ci/run_tests.jl
     agents:
@@ -49,7 +49,7 @@ steps:
   - label: ":macos: macos-aarch64"
     plugins:
       - JuliaCI/julia#v1:
-          version: "nightly"
+          version: "pre"
       - JuliaCI/julia-coverage#v1:
           codecov: true
     command: |
@@ -62,7 +62,7 @@ steps:
   - label: ":windows: windows-x86_64"
     plugins:
       - JuliaCI/julia#v1:
-          version: "nightly"
+          version: "pre"
       - JuliaCI/julia-coverage#v1:
           codecov: true
     command: |