fileperms: newer Go 1.13+ octal literal format

Problem: While removing cgroupsv1 code, I noticed my neovim Go config
automatically changed fileperms to the new octal format and I didn't
want that polluting my diffs.

Decision: I thought it best to switch to the new octal format in a dedicated PR.

Action:
- Cursor switched to new octal format for all fileperm ocurrences in Go
 source and test files.
- vendor/, docs/ and non-Go files were ignored.
- Reviewed manually.

Ref: https://go.dev/ref/spec#Go_1.13

Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>

internal/remote_build_helpers/utils_test.go

@@ -34,7 +34,7 @@ func TestTempFileManager(t *testing.T) {
 		secretPath := filepath.Join(tempdir, "secret.txt")
 
 		content := "test secret"
-		err := os.WriteFile(secretPath, []byte(content), 0600)
+		err := os.WriteFile(secretPath, []byte(content), 0o600)
 		assert.NoError(t, err)
 
 		filename, err := manager.CreateTempSecret(secretPath, tempdir)