.github: run tests on go 1.19, 1.20 and 1.21

Sicne we require go v1.19 now at minimum, we cannot run tests on go
v1.17 or v1.18 anymore.

Since there are more recent versions of Go available as well, we start
testing the packages on those versions in addition to 1.19.

.github/workflows/go-getter.yml

@@ -19,9 +19,9 @@ jobs:
     strategy:
       matrix:
         go-version:
-          - 1.17
-          - 1.18
           - 1.19
+          - "1.20"
+          - 1.21
         directory:
           - s3
           - gcs
@@ -110,9 +110,9 @@ jobs:
     strategy:
       matrix:
         go-version:
-          - 1.17
-          - 1.18
           - 1.19
+          - "1.20"
+          - 1.21
         directory:
           - s3
           - gcs
@@ -190,9 +190,9 @@ jobs:
     strategy:
       matrix:
         go-version:
-          - 1.17
-          - 1.18
           - 1.19
+          - "1.20"
+          - 1.21
     permissions:
       id-token: write
       contents: read