v0.6.2

Fixes:

• ssh: Fix file descriptor leak when doing SSH forwarding #1150
• contenthash: Fix bug with symlink in source path of a copy operation #1140
• fsutil: Handle copying unix sockets in local sources #1144
• llbsolver: Fix using multiple remote cache importers #1156
• http: Handle missing but unambiguous ETags in response #1159
• solver: Fix possible inefficient parallelization in solver #1166
• executor: oom_score_adj is no longer set from main process #1139