Replace matrix strategy with environment variable

[jongwooo]

What this PR does / why we need it:

Replaced matrix strategy ${{ matrix.go_version }} with environment variable ${{ env.GO_VERSION }}.

About matrix strategies
A matrix strategy lets you use variables in a single job definition to automatically create multiple job runs that are based on the combinations of the variables.

I think matrix is better for running multiple jobs; when running a single job, simply set the go version can be replaced with an environment variable. I've referenced the workflow in the link attached below: https://github.com/kubernetes/minikube/blob/master/.github/workflows/pr.yml#L13-L15

AS-IS

jobs:
  build:
    name: build
    strategy:
      matrix:
        go_version:
          - 1.19.2
    runs-on: ubuntu-latest
    steps:

    - name: Set up Go ${{ matrix.go_version }}
      uses: actions/setup-go@v3
      with:
        go-version: ${{ matrix.go_version }}

TO-BE

env:
  GO_VERSION: '1.19.2'

jobs:
  build:
    name: build
    runs-on: ubuntu-latest
    steps:

    - name: Set up Go ${{ env.GO_VERSION }}
      uses: actions/setup-go@v3
      with:
        go-version: ${{ env.GO_VERSION }}

Which issue(s) this PR fixes:

Fixes #618

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #619 (f392ca2) into main (cf74a80) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #619   +/-   ##
=======================================
  Coverage   50.23%   50.23%           
=======================================
  Files          69       69           
  Lines        7305     7305           
=======================================
  Hits         3670     3670           
  Misses       3145     3145           
  Partials      490      490           

[krapie]

Seems reasonable to me. Thank you for your contribution!