CI: Use SCU build for Linux w/ sanitizers build

It's the slowest build so a speedup from SCU is welcome.
The other purpose of this change is to actually catch global scope
conflicts which would break the SCU build.

SCU builds have drawbacks as they won't fully validate that the
includes are correct, but we should have enough other builds in the CI
build matrix to catch this type of bug.

.github/workflows/linux_builds.yml

@@ -34,12 +34,12 @@ jobs:
             artifact: true
             compat: true
 
-          - name: Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)
+          - name: Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)
             cache-name: linux-editor-double-sanitizers
             target: editor
             tests: true
             # Debug symbols disabled as they're huge on this build and we hit the 14 GB limit for runners.
-            sconsflags: dev_build=yes debug_symbols=no precision=double use_asan=yes use_ubsan=yes linker=gold
+            sconsflags: dev_build=yes scu_build=yes debug_symbols=no precision=double use_asan=yes use_ubsan=yes linker=gold
             proj-test: true
             # Can be turned off for PRs that intentionally break compat with godot-cpp,
             # until both the upstream PR and the matching godot-cpp changes are merged.