Bounce kubernetes testing versions

This update the test matrix to latest set of 3 minor k8s releases

Fixes: #347

Co-Authored-By: Jean-Philippe Evrard <open-source@a.spamming.party>

.github/workflows/on-pr.yaml

@@ -97,9 +97,9 @@ jobs:
       fail-fast: false
       matrix:
         kubernetes:
-          - "1.18"
           - "1.19"
           - "1.20"
+          - "1.21"
     steps:
       - uses: actions/checkout@v2
       - name: Find go version
@@ -169,7 +169,7 @@ jobs:
       fail-fast: false
       matrix:
         kubernetes:
-          - "1.20"
+          - "1.21"
     steps:
       - uses: actions/checkout@v2
       - name: Find go version

.github/workflows/periodics-daily.yaml

@@ -74,9 +74,9 @@ jobs:
     strategy:
       matrix:
         kubernetes:
-          - "1.18"
           - "1.19"
           - "1.20"
+          - "1.21"
     steps:
       - uses: actions/checkout@v2
       - name: Find go version
@@ -132,4 +132,4 @@ jobs:
         env:
           DEBUG: true
         run: |
-          ./tests/kind/follow-coordinated-reboot.sh
+          ./tests/kind/follow-coordinated-reboot.sh