[packaging] Run git gc to minimize .git disk footprint (#113467)

dev/bots/prepare_package.dart

@@ -418,6 +418,9 @@ class ArchiveCreator {
 
     // Make the origin point to github instead of the chromium mirror.
     await _runGit(<String>['remote', 'set-url', 'origin', githubRepo]);
+
+    // Minify `.git` footprint (saving about ~100 MB as of Oct 2022)
+    await _runGit(<String>['gc', '--prune=now', '--aggressive']);
   }
 
   /// Retrieve the MinGit executable from storage and unpack it.

dev/bots/test/prepare_package_test.dart

@@ -126,6 +126,7 @@ void main() {
           'git clone -b beta https://flutter.googlesource.com/mirrors/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
+          'git gc --prune=now --aggressive': null,
           'git describe --tags --exact-match $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
           '$flutter --version --machine': <ProcessResult>[
             ProcessResult(0, 0, '{"dartSdkVersion": "3.2.1"}', ''),
@@ -162,6 +163,7 @@ void main() {
           'git clone -b beta https://flutter.googlesource.com/mirrors/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
+          'git gc --prune=now --aggressive': null,
           'git describe --tags --exact-match $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
           '$flutter --version --machine': <ProcessResult>[
             ProcessResult(0, 0, '{"dartSdkVersion": "3.2.1"}', ''),
@@ -209,6 +211,7 @@ void main() {
           'git clone -b beta https://flutter.googlesource.com/mirrors/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
+          'git gc --prune=now --aggressive': null,
           'git describe --tags --exact-match $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
           '$flutter --version --machine': <ProcessResult>[
             ProcessResult(0, 0, '{"dartSdkVersion": "3.2.1"}', ''),
@@ -266,6 +269,7 @@ void main() {
           'git clone -b beta https://flutter.googlesource.com/mirrors/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
+          'git gc --prune=now --aggressive': null,
           'git describe --tags --abbrev=0 $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
           '$flutter --version --machine': <ProcessResult>[
             ProcessResult(0, 0, '{"dartSdkVersion": "3.2.1"}', ''),
@@ -315,6 +319,7 @@ void main() {
           'git clone -b beta https://flutter.googlesource.com/mirrors/flutter': null,
           'git reset --hard $testRef': null,
           'git remote set-url origin https://github.com/flutter/flutter.git': null,
+          'git gc --prune=now --aggressive': null,
           'git describe --tags --exact-match $testRef': <ProcessResult>[ProcessResult(0, 0, 'v1.2.3', '')],
           '$flutter --version --machine': <ProcessResult>[
             ProcessResult(0, 0, '{"dartSdkVersion": "3.2.1"}', ''),