internal/ci: bump to Go 1.21.5 for the upcoming release

We did v0.7.0-rc.1 with Go 1.21.4, and 1.21.5 was just released.
Might as well use it for the final v0.7.0 release.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>
Change-Id: I53978d1a50f0abd25604545278c833d7308da6bf
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1173212
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Paul Jolly <paul@myitcv.io>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

.github/workflows/release.yml

@@ -66,7 +66,7 @@ jobs:
         uses: actions/setup-go@v4
         with:
           cache: false
-          go-version: 1.21.4
+          go-version: 1.21.5
       - name: Setup qemu
         uses: docker/setup-qemu-action@v2
       - name: Set up Docker Buildx

internal/ci/repo/repo.cue

@@ -37,7 +37,7 @@ latestStableGo: "1.21.x"
 // Use a specific latest version for release builds.
 // Note that we don't want ".x" for the sake of reproducibility,
 // so we instead pin a specific Go release.
-pinnedReleaseGo: "1.21.4"
+pinnedReleaseGo: "1.21.5"
 
 goreleaserVersion: "v1.22.1"