ci(conformance): use go-version-file: go.mod to track project Go

Conformance jobs were pinned to Go 1.24, but PR #17 bumped go.mod
to require Go 1.26 (controller-runtime v0.24). All five conformance
jobs failed with: "go.mod requires go >= 1.26.0 (running go 1.24)".

Match what ci.yaml does: read the version from go.mod so the
workflow tracks future bumps automatically.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: stubbi

.github/workflows/conformance.yaml

@@ -20,7 +20,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
-        with: { go-version: "1.24" }
+        with: { go-version-file: go.mod }
       - uses: helm/kind-action@v1
         with:
           cluster_name: hermes-conformance
@@ -45,7 +45,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
-        with: { go-version: "1.24" }
+        with: { go-version-file: go.mod }
       - uses: helm/kind-action@v1
         with:
           cluster_name: hermes-conformance
@@ -70,7 +70,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
-        with: { go-version: "1.24" }
+        with: { go-version-file: go.mod }
       - uses: azure/setup-helm@v5
       - env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
@@ -83,7 +83,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
-        with: { go-version: "1.24" }
+        with: { go-version-file: go.mod }
       - uses: helm/kind-action@v1
         with:
           cluster_name: hermes-conformance
@@ -108,7 +108,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
-        with: { go-version: "1.24" }
+        with: { go-version-file: go.mod }
       - uses: helm/kind-action@v1
         with:
           cluster_name: hermes-conformance