repository: trigger GC after loading the index

Loading the index requires some scratch space, thus make sure that this
memory does not factor into the targeted gc memory usage limit.

internal/repository/repository.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"runtime"
 	"sort"
 	"sync"
 
@@ -601,6 +602,9 @@ func (r *Repository) LoadIndex(ctx context.Context) error {
 		return err
 	}
 
+	// Trigger GC to reset garbage collection threshold
+	runtime.GC()
+
 	if r.cfg.Version < 2 {
 		// sanity check
 		ctx, cancel := context.WithCancel(ctx)