build: Revert specifics for Go 1.21.4, build using Go 1.21.5 (#9264)

This reverts commit e477777.

In principle, we could have stayed with `~1.21.1`, but `check-latest:
true` apparently checks some cache/manifest/something that is only
periodically refreshed and isn't aware of 1.21.5 yet. So update the
constraints to force an upgrade.

Also the infrastructure images weren't actually using the constraint
since there was no `setup-go` action...

.github/workflows/build-infra-dockers.yaml

@@ -6,7 +6,7 @@ on:
       - infrastructure
 
 env:
-  GO_VERSION: "~1.21.1"
+  GO_VERSION: "~1.21.5"
   CGO_ENABLED: "0"
   BUILD_USER: docker
   BUILD_HOST: github.syncthing.net
@@ -28,6 +28,11 @@ jobs:
         with:
           fetch-depth: 0
 
+      - uses: actions/setup-go@v4
+        with:
+          go-version: ${{ env.GO_VERSION }}
+          check-latest: true
+
       - name: Login to Docker Hub
         uses: docker/login-action@v3
         with:

.github/workflows/build-syncthing.yaml

@@ -12,7 +12,7 @@ env:
   # The go version to use for builds. We set check-latest to true when
   # installing, so we get the latest patch version that matches the
   # expression.
-  GO_VERSION: "~1.21.1"
+  GO_VERSION: "~1.21.5"
 
   # Optimize compatibility on the slow archictures.
   GO386: softfloat
@@ -48,20 +48,7 @@ jobs:
         runner: ["windows-latest", "ubuntu-latest", "macos-latest"]
         # The oldest version in this list should match what we have in our go.mod.
         # Variables don't seem to be supported here, or we could have done something nice.
-        go: ["1.20", "1.21"]
-
-        # Don't run the Windows tests with Go 1.21.4 or 1.20.11; this can be
-        # removed when 1.21.5 and 1.20.12 is released.
-        exclude:
-          - runner: windows-latest
-            go: "1.20"
-          - runner: windows-latest
-            go: "1.21"
-        include:
-          - runner: windows-latest
-            go: "~1.20.12 || ~1.20.0 <1.20.11"
-          - runner: windows-latest
-            go: "~1.21.5 || ~1.21.1 <1.21.4"
+        go: ["~1.20.12", "~1.21.5"]
     runs-on: ${{ matrix.runner }}
     steps:
       - name: Set git to use LF
@@ -169,9 +156,7 @@ jobs:
 
       - uses: actions/setup-go@v4
         with:
-          # Temporary version constraint to avoid 1.21.4 which has a bug in
-          # path handling. This can be removed when 1.21.5 is released.
-          go-version: "~1.21.5 || ~1.21.1 <1.21.4"
+          go-version: ${{ env.GO_VERSION }}
           cache: false
           check-latest: true