nonspec: remove Joshua as a maintainer (slsa-framework#1234)

I haven't been able to attend meetings or make time to review changes in
some time, so it feels right that I stepp down.

Thanks so much for all the great collaboration. I will continue to
advocate for SLSA and wish the project every success.

---------

Signed-off-by: Joshua Lock <joshuagloe@gmail.com>

MAINTAINERS.md

@@ -18,7 +18,6 @@ permissions in this repository.
 | Aditya Sirish A Yelgundhalli | aditya.sirish@nyu.edu | @Aditya Sirish | [adityasaky](https://github.com/adityasaky) | New York University and Bloomberg
 | Andrew McNamara | arewm@redhat.com |  @arewm | [arewm](https://github.com/arewm) | Red Hat
 | Arnaud Le Hors | lehors@us.ibm.com | @Arnaud Le Hors | [lehors](https://github.com/lehors) | IBM
-| Joshua Lock | joshuagloe@gmail.com | @Joshua Lock |  [joshuagl](https://github.com/joshuagl) | Verizon
 | Marcela Melara | marcela.melara@intel.com | @Marcela Melara | [marcelamelara](https://github.com/marcelamelara) | Intel
 | Mark Lodato | lodato@google.com |  @Mark Lodato | [MarkLodato](https://github.com/MarkLodato) | Google
 | Michael Lieberman | mlieberman85@gmail.com | @Michael Lieberman | [mlieberman85](https://github.com/mlieberman85) | Kusari
@@ -54,6 +53,7 @@ candidate to the [Specification Maintainers] GitHub team.
 | Name | Email | OpenSSF Slack | GitHub | Affiliation
 | --- | --- | --- | --- | ---
 | Kris K | kkris@google.com | @Kris K | [kpk47](https://github.com/kpk47) | Google
+| Joshua Lock | joshuagloe@gmail.com | @Joshua Lock |  [joshuagl](https://github.com/joshuagl) | Verizon
 
 ### Removing a Maintainer