Update integration tests for the fs command

[pietern]

Changes

• Fix potential panic
• Reuse ctx variable

Why

I observed the following panic. The code could access r after a failed assertion here:

cli/integration/cmd/fs/cp_test.go

Lines 41 to 46 in fb2b646

	r, err := f.Read(ctx, relPath)
	assert.NoError(t, err)
	defer r.Close()
	b, err := io.ReadAll(r)
	require.NoError(t, err)
	assert.Equal(t, "abc", string(b))

=== FAIL: integration/cmd/fs TestFsCpFileToFile (99.64s)
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x11e4b13]

goroutine 344 [running]:
testing.tRunner.func1.2({0x1450540, 0x25334c0})
	/home/runner/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.2.linux-amd64/src/testing/testing.go:1734 +0x21c
testing.tRunner.func1()
	/home/runner/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.2.linux-amd64/src/testing/testing.go:1737 +0x35e
panic({0x1450540?, 0x25334c0?})
	/home/runner/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.2.linux-amd64/src/runtime/panic.go:792 +0x132
github.com/databricks/cli/integration/cmd/fs_test.assertTargetFile(0xc0004b4540, {0x19b5c60?, 0x2589080?}, {0x19bc0b0?, 0xc00111c980?}, {0x1734a1a?, 0xc0004b4540?})
	/home/runner/work/eng-dev-ecosystem/eng-dev-ecosystem/ext/cli/integration/cmd/fs/cp_test.go:43 +0x93
github.com/databricks/cli/integration/cmd/fs_test.TestFsCpFileToFile.func1(0xc0004b4540)
	/home/runner/work/eng-dev-ecosystem/eng-dev-ecosystem/ext/cli/integration/cmd/fs/cp_test.go:158 +0x2a5
testing.tRunner(0xc0004b4540, 0xc000551170)
	/home/runner/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.2.linux-amd64/src/testing/testing.go:1792 +0xf4
created by testing.(*T).Run in goroutine 96
	/home/runner/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.24.2.linux-amd64/src/testing/testing.go:1851 +0x413

Tests

Tests still pass.

[pietern]

Integration test failures unrelated.