CI: Reduce Actions cache pressure in ResInsightWithCache

Only save the buildcache from the default branch. GitHub scopes cache writes to the current ref, so a cache saved from a feature branch or PR is invisible to every other branch while still counting against the 10 GB per-repository quota and evicting the shared caches on the default branch.

Disable unity build for all configurations. Unity blobs invalidate on any change to the sources they bundle, which defeats buildcache reuse and fills the cache with objects that are unlikely to be hit again.

.github/workflows/ResInsightWithCache.yml

@@ -28,7 +28,6 @@ jobs:
               build-python-module: true,
               execute-unit-tests: true,
               execute-pytests: true,
-              unity-build: true,
               publish-to-pypi: false,
               enable-asserts: false,
               vcpkg-bootstrap: bootstrap-vcpkg.bat,
@@ -43,7 +42,6 @@ jobs:
               build-python-module: true,
               execute-unit-tests: true,
               execute-pytests: true,
-              unity-build: false,
               publish-to-pypi: true,
               enable-asserts: false,
               vcpkg-bootstrap: bootstrap-vcpkg.sh,
@@ -58,7 +56,6 @@ jobs:
               build-python-module: true,
               execute-unit-tests: true,
               execute-pytests: false,
-              unity-build: false,
               publish-to-pypi: false,
               enable-asserts: true,
               vcpkg-bootstrap: bootstrap-vcpkg.sh,
@@ -273,7 +270,7 @@ jobs:
           -DRESINSIGHT_INCLUDE_APPLICATION_UNIT_TESTS=true
           -DRESINSIGHT_TREAT_WARNINGS_AS_ERRORS=true
           -DRESINSIGHT_ENABLE_PRECOMPILED_HEADERS=false
-          -DRESINSIGHT_ENABLE_UNITY_BUILD=${{ matrix.config.unity-build }}
+          -DRESINSIGHT_ENABLE_UNITY_BUILD=false
           -DRESINSIGHT_ENABLE_ASSERTS_IN_RELEASE=${{ matrix.config.enable-asserts }}
           -DRESINSIGHT_ENABLE_GRPC=${{ matrix.config.build-python-module }}
           -DRESINSIGHT_GRPC_PYTHON_EXECUTABLE=${{ steps.python-path.outputs.PYTHON_EXECUTABLE }}
@@ -293,7 +290,16 @@ jobs:
         # Save the cache with the current date, unless a cache for the current
         # date was already restored (cache keys are immutable and cannot be
         # overwritten)
-        if: steps.cache-buildcache.outputs.cache-hit != 'true'
+        #
+        # Only save from the default branch. GitHub scopes cache writes to the
+        # current ref, and a branch can only read its own scope plus the default
+        # branch, so a cache saved from a feature branch or PR is invisible to
+        # every other branch. Those copies bring no reuse, but they do count
+        # against the 10 GB per-repository quota and evict the shared caches on
+        # the default branch.
+        if: >-
+          steps.cache-buildcache.outputs.cache-hit != 'true' &&
+          github.ref == format('refs/heads/{0}', github.event.repository.default_branch)
         uses: actions/cache/save@v6
         with:
           path: ${{ env.BUILDCACHE_DIR }}