all: Fix various user-facing and non-user-facing typos (#8509)

Found via `codespell -q 3 -S lang,./gui/default/vendor -L benchs,bu,inflight,ro`

lib/fs/basicfs_fileinfo_windows.go

@@ -37,7 +37,7 @@ func (e basicFileInfo) Mode() FileMode {
 		// NTFS deduped files. Remove the symlink bit.
 		m &^= os.ModeSymlink
 	}
-	// Set executable bits on files with executable extenions (.exe, .bat, etc).
+	// Set executable bits on files with executable extensions (.exe, .bat, etc).
 	if isWindowsExecutable(e.Name()) {
 		m |= 0111
 	}

lib/fs/casefs_test.go

@@ -242,7 +242,7 @@ func benchmarkWalkFakeFS(b *testing.B, fsys Filesystem, paths []string, otherOpE
 }
 
 func TestStressCaseFS(t *testing.T) {
-	// Exercise a bunch of paralell operations for stressing out race
+	// Exercise a bunch of parallel operations for stressing out race
 	// conditions in the realnamer cache etc.
 
 	const limit = 10 * time.Second

lib/fs/mtimefs_test.go

@@ -205,7 +205,7 @@ func TestMtimeFSInsensitive(t *testing.T) {
 			t.Error("Should not have failed:", err)
 		}
 
-		// Check that we get back the mtime we set, if we were supposed to succed.
+		// Check that we get back the mtime we set, if we were supposed to succeed.
 		info, err := fs.Lstat("testdata/FILE")
 		if err != nil {
 			t.Error("Lstat shouldn't fail:", err)