python-installer: patch behavior for when script file exists #21196

Job	Run time
Feeds Package Test Build / Test aarch64_generic	4m 0s
Feeds Package Test Build / Test arm_cortex-a15_neon-vfpv4	2m 35s
Feeds Package Test Build / Test arm_cortex-a9_vfpv3-d16	3m 18s
Feeds Package Test Build / Test i386_pentium-mmx	3m 58s
Feeds Package Test Build / Test mips_24kc	2m 46s
Feeds Package Test Build / Test mipsel_24kc	4m 8s
Feeds Package Test Build / Test powerpc_464fp	4m 8s
Feeds Package Test Build / Test powerpc_8548	2m 51s
Feeds Package Test Build / Test riscv64_riscv64	3m 23s
Feeds Package Test Build / Test x86_64	4m 15s
	35m 22s

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