fix: more explicit typing for conver flags

Author: shetzel

package.json

@@ -11,7 +11,7 @@
     "@salesforce/core": "^8.8.5",
     "@salesforce/kit": "^3.2.3",
     "@salesforce/plugin-info": "^3.4.47",
-    "@salesforce/sf-plugins-core": "^12.2.0",
+    "@salesforce/sf-plugins-core": "^12.2.1",
     "@salesforce/source-deploy-retrieve": "12.16.9",
     "@salesforce/source-tracking": "^7.3.19",
     "@salesforce/ts-types": "^2.0.12",

src/commands/project/convert/source.ts

@@ -39,7 +39,10 @@ export class Source extends SfCommand<ConvertResultJson> {
   public static readonly aliases = ['force:source:convert'];
   public static readonly deprecateAliases = true;
   public static readonly flags = {
-    'api-version': { ...orgApiVersionFlagWithDeprecations, summary: messages.getMessage('flags.api-version.summary') },
+    'api-version': {
+      ...orgApiVersionFlagWithDeprecations,
+      summary: messages.getMessage('flags.api-version.summary'),
+    } as Interfaces.OptionFlag<string | undefined, Interfaces.CustomOptions>,
     loglevel,
     'root-dir': Flags.directory({
       aliases: ['rootdir'],