build: upgrade Go toolchain to 1.26.4 project-wide (#14)

Bump libcore/go.mod toolchain directive (go1.24.9 -> go1.26.4) and all CI
setup-go pins (1.24.9 -> 1.26.4). The go.mod language floor (go 1.24.7) is
left as-is.

Verified the native core (starifly/sing-box + libneko + gomobile + all deps)
builds cleanly under Go 1.26.4 on the Linux builder.

Author: hawkff

.github/workflows/build.yml

@@ -30,7 +30,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Native Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib core
@@ -53,7 +53,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Mieru Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib mieru

.github/workflows/ci.yml

@@ -35,7 +35,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Native Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib core
@@ -58,7 +58,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Mieru Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib mieru

.github/workflows/preview.yml

@@ -26,7 +26,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Native Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib core
@@ -49,7 +49,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Mieru Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib mieru

.github/workflows/release.yml

@@ -32,7 +32,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Native Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib core
@@ -55,7 +55,7 @@ jobs:
         if: steps.cache.outputs.cache-hit != 'true'
         uses: actions/setup-go@v6
         with:
-          go-version: '1.24.9'
+          go-version: '1.26.4'
       - name: Mieru Build
         if: steps.cache.outputs.cache-hit != 'true'
         run: ./run lib mieru

libcore/go.mod

@@ -2,7 +2,7 @@ module libcore
 
 go 1.24.7
 
-toolchain go1.24.9
+toolchain go1.26.4
 
 require (
 	github.com/dyhkwong/sing-juicity v0.0.3