Update workflow to support Go 1.23

This commit adjusts the GitHub Actions workflow to include Go 1.23 in the matrix of supported versions. It also updates conditional steps for sendmail installation and coverage upload to reflect the new Go version.

.github/workflows/codecov.yml

@@ -36,7 +36,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        go: [1.18, 1.19, '1.20', '1.21', '1.22']
+        go: ['1.20', '1.21', '1.22', '1.23']
     steps:
     - name: Harden Runner
       uses: step-security/harden-runner@5c7944e73c4c2a096b17a9cb74d65b6c2bbafbde # v2.9.1
@@ -50,14 +50,14 @@ jobs:
       with:
         go-version: ${{ matrix.go }}
     - name: Install sendmail
-      if: matrix.go == '1.22' && matrix.os == 'ubuntu-latest'
+      if: matrix.go == '1.23' && matrix.os == 'ubuntu-latest'
       run: |
         sudo apt-get -y install sendmail; which sendmail
     - name: Run Tests
       run: |
         go test -v -race --coverprofile=coverage.coverprofile --covermode=atomic ./...
     - name: Upload coverage to Codecov
-      if: success() && matrix.go == '1.22' && matrix.os == 'ubuntu-latest'
+      if: success() && matrix.go == '1.23' && matrix.os == 'ubuntu-latest'
       uses: codecov/codecov-action@e28ff129e5465c2c0dcc6f003fc735cb6ae0c673 # v4.5.0
       with:
         token: ${{ secrets.CODECOV_TOKEN }} # not required for public repos