installer.iss: use x64 not x64compatible (6.2.2 compat)

Inno Setup 6.2.2 (pinned because innoextract 1.9 in Debian trixie
can't parse 6.3+ headers) doesn't recognise the 'x64compatible'
keyword. Use the legacy 'x64' which works across 6.0-6.7.

Failure: 'Error on line 25 in installer.iss: Value of [Setup]
section directive ArchitecturesAllowed is invalid' (run #11).

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

installer/installer.iss

@@ -22,8 +22,11 @@ Compression=lzma2
 SolidCompression=yes
 WizardStyle=modern
 PrivilegesRequired=admin
-ArchitecturesAllowed=x64compatible
-ArchitecturesInstallIn64BitMode=x64compatible
+; "x64compatible" is Inno Setup 6.3+ syntax. Our CI uses 6.2.2 (last
+; version still parsed by innoextract 1.9 in Debian trixie), so use
+; the legacy "x64" keyword which works on 6.0 through 6.7.
+ArchitecturesAllowed=x64
+ArchitecturesInstallIn64BitMode=x64
 LicenseFile=..\LICENSE
 MinVersion=10.0.17763
 UninstallDisplayName=Drover-Go {#MyAppVersion}