Disable `String#to_f` special number specs on MSYS2 MINGW64 environment #12764

Job	Run time
x86_64-gnu-test (1.7.3)	34m 23s
x86_64-gnu-test-preview_mt	5m 35s
x86_64-gnu-test (1.8.2)	33m 44s
x86_64-gnu-test (1.9.2)	34m 35s
x86_64-gnu-test (1.10.1)	35m 37s
x86_64-gnu-test (1.11.2)	37m 9s
x86_64-gnu-test (1.12.2)	34m 24s
x86_64-gnu-test (1.13.3)	35m 56s
x86_64-gnu-test (1.14.0)	33m 35s
check_format	1m 36s
x86_64-musl-test	35m 39s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 30s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	35m 6s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	33m 17s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	36m 28s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	35m 31s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	37m 11s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	33m 18s
	9h 26m 34s

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