ci: disable freebsd 13.0 builds (due to issues in the image)

Before it fails with:

   exec ssh: pkg install -y  mbedtls cmake python3
    /bin/bash /Users/runner/work/_actions/vmactions/freebsd-vm/v0/run.sh execSSH
    Config file: freebsd-13.0.conf
    Pseudo-terminal will not be allocated because stdin is not a terminal.
    Warning: no access to tty (Bad file descriptor).
    Thus no job control in this shell.
    Installing pkg-1.18.3...
    Newer FreeBSD version for package pkg:
    To ignore this error set IGNORE_OSVERSION=yes
    - package: 1301000
    - running kernel: 1300139
    Ignore the mismatch and continue? [y/N]:
    Failed to install the following 1 package(s): /tmp//pkg.txz.18yvwm
    Bootstrapping pkg from pkg+http://pkg.FreeBSD.org/FreeBSD:13:amd64/quarterly, please wait...
    Verifying signature with trusted certificate pkg.freebsd.org.2013102301... done
    Error: The process '/bin/bash' failed with exit code 1

And now with:
  ld-elf.so.1: /lib/libc.so.7: version FBSD_1.7 required by /usr/local/lib/libpython3.9.so.1.0 not found

Commenting for now, anyway we do not need such huge CI matrix, because
we have only public workers, and they are pretty busy.

Cc: @Neilpang

.github/workflows/build.yml

@@ -746,7 +746,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        release: ["12.3", "13.0", "13.1"]
+        # NOTE: 13.0 has some issues:
+        #   ld-elf.so.1: /lib/libc.so.7: version FBSD_1.7 required by /usr/local/lib/libpython3.9.so.1.0 not found
+        release: ["12.3", "13.1"]
         EVENT_MATRIX:
           - NONE
           - NO_SSL
@@ -840,7 +842,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        release: ["12.3", "13.0", "13.1"]
+        # NOTE: 13.0 has some issues:
+        #   ld-elf.so.1: /lib/libc.so.7: version FBSD_1.7 required by /usr/local/lib/libpython3.9.so.1.0 not found
+        release: ["12.3", "13.1"]
         EVENT_MATRIX:
           - NONE
           - NO_SSL