CI: Speed up merge checks: linux only, no coverage (#3917)

## Why
Reduce waiting for merge queue. We still run full tests on PR (without
coverage) and on every commit to main with coverage.

Author: denik

.github/workflows/push.yml

@@ -38,10 +38,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os:
-          - macos-latest
-          - ubuntu-latest
-          - windows-latest
+        os: ${{ github.event_name == 'merge_group' && fromJSON('["ubuntu-latest"]') || fromJSON('["macos-latest", "ubuntu-latest", "windows-latest"]') }}
         deployment:
           - "terraform"
           - "direct"
@@ -83,17 +80,17 @@ jobs:
           pip3 install wheel==0.45.1
 
       - name: Run tests without coverage
-        # We run tests without coverage on PR because we don't make use of coverage information
+        # We run tests without coverage on PR, merge_group, and schedule because we don't make use of coverage information
         # and would like to run the tests as fast as possible. We run it on schedule as well, because that is what
         # populates the cache and cache may include test results.
-        if: ${{ github.event_name == 'pull_request' || github.event_name == 'schedule' }}
+        if: ${{ github.event_name == 'pull_request' || github.event_name == 'merge_group' || github.event_name == 'schedule' }}
         env:
           ENVFILTER: DATABRICKS_BUNDLE_ENGINE=${{ matrix.deployment }}
         run: make test
 
       - name: Run tests with coverage
-        # Still run 'make cover' on push to main and merge checks to make sure it does not get broken.
-        if: ${{ github.event_name != 'pull_request' && github.event_name != 'schedule' }}
+        # Only run 'make cover' on push to main to make sure it does not get broken.
+        if: ${{ github.event_name == 'push' }}
         env:
           ENVFILTER: DATABRICKS_BUNDLE_ENGINE=${{ matrix.deployment }}
         run: make cover