Filter flaky counts in sync_build_isolation_extra (#7531)

I've seen this flake several times now, e.g.,
https://github.com/astral-sh/uv/actions/runs/10933201998/job/30351289277?pr=7530

I don't quite understand why, but we have a standard filter for this.

crates/uv/tests/sync.rs

@@ -632,7 +632,7 @@ fn sync_build_isolation_package() -> Result<()> {
 /// Use dedicated extra groups to install dependencies for `--no-build-isolation-package`.
 #[test]
 fn sync_build_isolation_extra() -> Result<()> {
-    let context = TestContext::new("3.12");
+    let context = TestContext::new("3.12").with_filtered_counts();
 
     let pyproject_toml = context.temp_dir.child("pyproject.toml");
     pyproject_toml.write_str(
@@ -666,7 +666,7 @@ fn sync_build_isolation_extra() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    Resolved 7 packages in [TIME]
+    Resolved [N] packages in [TIME]
     error: Failed to prepare distributions
       Caused by: Failed to fetch wheel: source-distribution @ https://files.pythonhosted.org/packages/10/1f/57aa4cce1b1abf6b433106676e15f9fa2c92ed2bd4cf77c3b50a9e9ac773/source_distribution-0.0.1.tar.gz
       Caused by: Build backend failed to build wheel through `build_wheel()` with exit status: 1
@@ -686,7 +686,7 @@ fn sync_build_isolation_extra() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    Resolved 7 packages in [TIME]
+    Resolved [N] packages in [TIME]
     error: Failed to prepare distributions
       Caused by: Failed to fetch wheel: source-distribution @ https://files.pythonhosted.org/packages/10/1f/57aa4cce1b1abf6b433106676e15f9fa2c92ed2bd4cf77c3b50a9e9ac773/source_distribution-0.0.1.tar.gz
       Caused by: Build backend failed to build wheel through `build_wheel()` with exit status: 1
@@ -706,9 +706,9 @@ fn sync_build_isolation_extra() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    Resolved 7 packages in [TIME]
-    Prepared 6 packages in [TIME]
-    Installed 6 packages in [TIME]
+    Resolved [N] packages in [TIME]
+    Prepared [N] packages in [TIME]
+    Installed [N] packages in [TIME]
      + hatchling==1.22.4
      + packaging==24.0
      + pathspec==0.12.1
@@ -724,10 +724,10 @@ fn sync_build_isolation_extra() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    Resolved 7 packages in [TIME]
-    Prepared 1 package in [TIME]
-    Uninstalled 5 packages in [TIME]
-    Installed 1 package in [TIME]
+    Resolved [N] packages in [TIME]
+    Prepared [N] packages in [TIME]
+    Uninstalled [N] packages in [TIME]
+    Installed [N] packages in [TIME]
      - hatchling==1.22.4
      - packaging==24.0
      - pathspec==0.12.1