Miscellaneous workflow updates (#165)

# Description

Split off from other contemporary PRs as these changes are better suited
to be outside them. In specific, this PR makes the following changes:

- sets `fail-fast: false` so that we run both jobs in the test matrix
- runs on pushes to the main branch only, as we were otherwise running
workflows twice: one for the push event and one for the pull request
event
- modifies the concurrency setting to cancel intermediate runs for both

Author: agriyakhetarpal

.github/workflows/main.yml

@@ -2,10 +2,12 @@ name: CI
 
 on:
   push:
+    branches:
+      - main
   pull_request:
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
 env:
@@ -19,6 +21,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
+      fail-fast: false
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2