github: bump the versions in the GH actions

According to the Go release policy[1], only the two most recent
releases are supported:

  Each major Go release is supported until there are two newer
  major releases. For example, Go 1.5 was supported until the
  Go 1.7 release, and Go 1.6 was supported until the Go 1.8
  release. We fix critical problems, including critical
  security problems, in supported releases as needed by
  issuing minor revisions (for example, Go 1.6.1, Go 1.6.2,
  and so on).

... and with Go v1.18 being the most recent major release, trim the
Go versions to the two supported 1.18.x and 1.17.x, leaving 1.16.x
as it remains part of the GH Ubuntu 20.04 environment even though
it is officially unsupported.  Go 1.15.x is dropped from the test
matrix.

We also update the core libseccomp library to the latest v2.5.x
release, which is v2.5.4 as of April 21, 2022.  The previous
libseccomp versions are left untouched in the test matrix, even
though they are no longer supported upstream.

[1] https://go.dev/doc/devel/release#policy

Acked-by: Tom Hromatka <tom.hromatka@oracle.com>
Acked-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

.github/workflows/test.yml

@@ -15,8 +15,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go-version: [1.15.x, 1.16.x, 1.17.x]
-        libseccomp: ["v2.3.3", "v2.4.3", "v2.5.2", "HEAD"]
+        go-version: [1.16.x, 1.17.x, 1.18.x]
+        libseccomp: ["v2.3.3", "v2.4.3", "v2.5.4", "HEAD"]
 
     steps: