ci(openbsd): don't specify versions for dependencies if possible

It's more convenient to not specify the version and let openbsd's
package manager figure it out. This will help us avoid manually bumping
dependency versions when a new version of openbsd is released.

Some packages have multiple versions and not specifying a version in
those cases fails the CI job, so providing a version seems to be
necessary for some key packages.

.builds/openbsd.yml

@@ -6,11 +6,11 @@ packages:
 - autoconf-2.71
 - automake-1.16.3
 - cmake
-- gettext-runtime-0.21p1
-- gettext-tools-0.21p1
+- gettext-runtime
+- gettext-tools
 - gmake
 - libtool
-- ninja-1.10.2p0
+- ninja
 - unzip-6.0p14
 - gdb