ci: rename "pr title check" workflow and job (#4962)

[I did this a while back for
osv-scanner](google/osv-scanner#2527) so might
as well do it here too:

> Maybe it's just me but I always get this workflow file confused with
the `checks` one. I've also adjusted the names so that they (imo)
present a bit clearer - they should show up as "Title / check" rather
than "OSV PR format check / Validate PR title"

Author: G-Rath

.github/workflows/pr-check.yml .github/workflows/title.yml.github/workflows/pr-check.yml renamed to .github/workflows/title.yml

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-name: OSV PR format check
+name: Title
 
 on:
   # `pull_request_target` is only required when editing PRs from forks.