ci: add pull request filter (#631)

Certains steps should be executed within the context of a pull request only.

.github/workflows/build.yml

@@ -51,7 +51,7 @@ jobs:
         fail_ci_if_error: true
 
     - name: Run Basic Test Results Action
-      if: ${{ !cancelled() }}
+      if: ${{ !cancelled() && github.event_name == 'pull_request' }}
       uses: codecov/basic-test-results@v1
       with:
         github-token: ${{ secrets.GITHUB_TOKEN }}
@@ -60,7 +60,7 @@ jobs:
 
     # TODO: Download release asset action with cache
     - name: Download latest released Sablier binary
-      if: ${{ !cancelled() }}
+      if: ${{ !cancelled() && github.event_name == 'pull_request'  }}
       id: latest-release
       run: |
         release_data=$(curl -s https://api.github.com/repos/sablierapp/sablier/releases/latest)
@@ -70,7 +70,7 @@ jobs:
         echo "artifact_path=sablier_${version}_linux-amd64" >> $GITHUB_OUTPUT
 
     - name: Compare the downloaded binary with the built binary
-      if: ${{ !cancelled() }}
+      if: ${{ !cancelled() && github.event_name == 'pull_request'  }}
       id: diff
       run: |
         go tool gsa -o diff.txt ${{ steps.latest-release.outputs.artifact_path }} sablier_draft_linux-amd64
@@ -79,7 +79,7 @@ jobs:
         echo "EOF" >> $GITHUB_OUTPUT
 
     - name: Comment diff on pull request
-      if: ${{ !cancelled() }}
+      if: ${{ !cancelled() && github.event_name == 'pull_request'  }}
       uses: thollander/actions-comment-pull-request@v3
       with:
         message: |