ci: replace setup-go action with manual Go install from go.dev

actions/setup-go@v5 was failing silently (0s steps) likely due to
network issues downloading Go from GitHub. Install Go directly from
go.dev which is more accessible.

Also remove Docker job (not needed yet) and simplify to 3 jobs.

.gitea/workflows/ci.yml

@@ -17,10 +17,12 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: go.mod
-          cache: true
+      - name: Install Go
+        run: |
+          GO_VERSION=$(grep '^go ' go.mod | awk '{print $2}')
+          curl -sL "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" | tar -C /usr/local -xzf -
+          echo "/usr/local/go/bin" >> $GITHUB_PATH
+          echo "$(go env GOPATH)/bin" >> $GITHUB_PATH
 
       - name: Check formatting
         run: |
@@ -43,10 +45,11 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: go.mod
-          cache: true
+      - name: Install Go
+        run: |
+          GO_VERSION=$(grep '^go ' go.mod | awk '{print $2}')
+          curl -sL "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" | tar -C /usr/local -xzf -
+          echo "/usr/local/go/bin" >> $GITHUB_PATH
 
       - name: Run unit tests
         run: go test -race -count=1 ./internal/...
@@ -60,26 +63,14 @@ jobs:
         with:
           fetch-depth: 0
 
-      - uses: actions/setup-go@v5
-        with:
-          go-version-file: go.mod
-          cache: true
+      - name: Install Go
+        run: |
+          GO_VERSION=$(grep '^go ' go.mod | awk '{print $2}')
+          curl -sL "https://go.dev/dl/go${GO_VERSION}.linux-amd64.tar.gz" | tar -C /usr/local -xzf -
+          echo "/usr/local/go/bin" >> $GITHUB_PATH
 
       - name: Build
         run: make build
 
       - name: Verify binary
         run: ./bin/lolly --help
-
-  docker:
-    name: Docker
-    needs: build
-    if: github.event_name == 'push'
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-
-      - uses: docker/setup-buildx-action@v3
-
-      - name: Build Docker image
-        run: docker build -t lolly:latest .