Increase minimum Go version to 1.26.3

As part of supporting uid/gid-mapped mounts, we need (*Process).WithHandle,
added in Go 1.26. We can bump the Go version now to catch any issues that may
arise.

PiperOrigin-RevId: 921600692

Author: relkochta

go.mod

@@ -1,6 +1,6 @@
 module gvisor.dev/gvisor
 
-go 1.25.5
+go 1.26.3
 
 require (
 	cloud.google.com/go/auth v0.20.0

tools/build_cover.sh

@@ -33,7 +33,7 @@ export GOMODCACHE GOCACHE
   # The gVisor code coverage implementation uses internal packages. More details
   # can be found here: https://github.com/golang/go/issues/76098.
 
-  go_version=1.25.5
+  go_version=1.26.3
 
   go_base_url="https://dl.google.com/go/go${go_version}"
   arch="$(uname -m)"

tools/go-allow-internal.patch

@@ -1,11 +1,11 @@
 diff --git a/src/cmd/go/internal/load/pkg.go b/src/cmd/go/internal/load/pkg.go
-index 1f791546f9..809e5f142b 100644
+index e2a77d7..fec9756 100644
 --- a/src/cmd/go/internal/load/pkg.go
 +++ b/src/cmd/go/internal/load/pkg.go
-@@ -1464,6 +1464,7 @@ func reusePackage(p *Package, stk *ImportStack) *Package {
+@@ -1465,6 +1465,7 @@ func reusePackage(p *Package, stk *ImportStack) *Package {
  // If the import is allowed, disallowInternal returns the original package p.
  // If not, it returns a new package containing just an appropriate error.
- func disallowInternal(ctx context.Context, srcDir string, importer *Package, importerPath string, p *Package, stk *ImportStack) *PackageError {
+ func disallowInternal(loaderstate *modload.State, ctx context.Context, srcDir string, importer *Package, importerPath string, p *Package, stk *ImportStack) *PackageError {
 +	return nil
  	// golang.org/s/go14internal:
  	// An import of a path containing the element “internal”