Skip IPv6 tests when TCLSH version is < 8.6 (#910)

In #786, we did skip it in the daily, but not for the others.
When running ./runtest on MacOS, we will get the failure.
```
couldn't open socket: host is unreachable (nodename nor servname provided, or not known)
```

The reason is that TCL 8.5 doesn't support ipv6, so we skip tests
tagged with ipv6. This also revert #786.

Signed-off-by: Binbin <binloveplay1314@qq.com>

.github/workflows/daily.yml

@@ -938,7 +938,7 @@ jobs:
         run: make SERVER_CFLAGS='-Werror'
       - name: test
         if: true && !contains(github.event.inputs.skiptests, 'valkey')
-        run: ./runtest --accurate --verbose --tags -ipv6 --clients 1 --no-latency --dump-logs ${{github.event.inputs.test_args}}
+        run: ./runtest --accurate --verbose --clients 1 --no-latency --dump-logs ${{github.event.inputs.test_args}}
       - name: module api test
         if: true && !contains(github.event.inputs.skiptests, 'modules')
         run: CFLAGS='-Werror' ./runtest-moduleapi --verbose --clients 1 --no-latency --dump-logs ${{github.event.inputs.test_args}}

tests/support/server.tcl

@@ -241,6 +241,11 @@ proc tags_acceptable {tags err_return} {
         return 0
     }
 
+    if {$::tcl_version < 8.6 && [lsearch $tags "ipv6"] >= 0} {
+        set err "TCL version is too low and does not support this"
+        return 0
+    }
+
     return 1
 }