GPG Path broken on GitHub Actions, resulting in builds fail

### Affected version

current master

### Bug description

Raised from #321 (but it fails since months, see other PRs)

GPG-Path on Github Action is broken, making builds fail

> we have in params: `--homedir D:\a\maven-gpg-plugin\maven-gpg-plugin\target\test-classes\gnupg` but in log is

```
gpg: keyblock resource '/d/a/maven-gpg-plugin/maven-gpg-plugin/target/it/no-main-artifact/D:\\a\\maven-gpg-plugin\\maven-gpg-plugin\\target\\test-classes\\gnupg/pubring.kbx': No such file or directory
```

```
[DEBUG] GPG Version: 2.4.9
[DEBUG] CMD: cmd.exe /X /C "gpg.exe --homedir D:\a\maven-gpg-plugin\maven-gpg-plugin\target\test-classes\gnupg --batch --pinentry-mode loopback --passphrase-fd 0 --armor --detach-sign --status-fd 1 --batch --no-tty --output D:\a\maven-gpg-plugin\maven-gpg-plugin\target\it\sign-with-passphase-from-maven-settings\target\test-1.0.pom.asc D:\a\maven-gpg-plugin\maven-gpg-plugin\target\it\sign-with-passphase-from-maven-settings\target\test-1.0.pom"
[GNUPG:] ERROR add_keyblock_resource 33587281
gpg: keyblock resource '/d/a/maven-gpg-plugin/maven-gpg-plugin/target/it/sign-with-passphase-from-maven-settings/D:\\a\\maven-gpg-plugin\\maven-gpg-plugin\\target\\test-classes\\gnupg/pubring.kbx': No such file or directory
```

Start by reproducing the GPG signing integration-test failure on GitHub Actions using the current master and the logged gpg command. Trace how the Windows --homedir path is passed to gpg.exe; done means the path is not prefixed or concatenated incorrectly and the affected builds pass.

Written by the indexing model from the issue text.