fix(ci): diff_check should not fail when all files are filtered

[krystofwoldrich]

This PR fixes skip-ci jobs which failed when only *.md files were changed.

grep -v '\.md$' returns code 1 when all lines are filtered out.

#skip-changelog

[github-actions]

Android (legacy) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	407.18 ms	431.10 ms	23.92 ms
Size	17.73 MiB	19.91 MiB	2.17 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d197b5c+dirty	338.94 ms	354.87 ms	15.93 ms
acadc0f+dirty	373.24 ms	381.51 ms	8.27 ms
9a3ca65+dirty	326.93 ms	330.14 ms	3.21 ms
ad6c299	375.94 ms	382.02 ms	6.08 ms
9433f35	347.64 ms	356.22 ms	8.58 ms
d7401ac+dirty	375.20 ms	383.51 ms	8.31 ms
15c80ab+dirty	336.27 ms	350.58 ms	14.31 ms
86d6d2c+dirty	332.90 ms	352.45 ms	19.55 ms
3853f43	329.68 ms	346.32 ms	16.64 ms
22e31b6	396.48 ms	419.64 ms	23.16 ms

App size

Revision	Plain	With Sentry	Diff
d197b5c+dirty	17.73 MiB	20.04 MiB	2.31 MiB
acadc0f+dirty	17.73 MiB	19.75 MiB	2.01 MiB
9a3ca65+dirty	17.73 MiB	20.04 MiB	2.31 MiB
ad6c299	17.73 MiB	19.75 MiB	2.02 MiB
9433f35	17.73 MiB	19.81 MiB	2.08 MiB
d7401ac+dirty	17.73 MiB	19.75 MiB	2.02 MiB
15c80ab+dirty	17.73 MiB	20.04 MiB	2.31 MiB
86d6d2c+dirty	17.73 MiB	20.04 MiB	2.31 MiB
3853f43	17.73 MiB	19.81 MiB	2.08 MiB
22e31b6	17.73 MiB	19.84 MiB	2.10 MiB

[github-actions]

Android (new) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	424.46 ms	444.48 ms	20.02 ms
Size	7.15 MiB	8.18 MiB	1.03 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
abb7058+dirty	320.78 ms	324.08 ms	3.30 ms
8900e1a+dirty	371.40 ms	377.70 ms	6.31 ms
e5c9b8b+dirty	335.40 ms	360.06 ms	24.67 ms
575f9da+dirty	337.15 ms	370.47 ms	33.32 ms
e73f4ed+dirty	262.98 ms	311.02 ms	48.04 ms
acadc0f+dirty	259.04 ms	304.67 ms	45.63 ms
dadc233+dirty	363.19 ms	370.37 ms	7.18 ms
34aba08+dirty	331.79 ms	376.69 ms	44.91 ms
12427f4+dirty	379.48 ms	400.92 ms	21.44 ms
457e29f+dirty	591.49 ms	612.96 ms	21.47 ms

App size

Revision	Plain	With Sentry	Diff
abb7058+dirty	7.15 MiB	8.10 MiB	980.40 KiB
8900e1a+dirty	7.15 MiB	8.03 MiB	901.79 KiB
e5c9b8b+dirty	7.15 MiB	8.10 MiB	980.41 KiB
575f9da+dirty	7.15 MiB	8.10 MiB	979.68 KiB
e73f4ed+dirty	7.15 MiB	8.09 MiB	965.94 KiB
acadc0f+dirty	7.15 MiB	8.03 MiB	903.20 KiB
dadc233+dirty	7.15 MiB	8.04 MiB	910.84 KiB
34aba08+dirty	7.15 MiB	8.07 MiB	946.13 KiB
12427f4+dirty	7.15 MiB	8.12 MiB	997.78 KiB
457e29f+dirty	7.15 MiB	8.10 MiB	981.29 KiB

[github-actions]

iOS (legacy) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1198.31 ms	1204.76 ms	6.45 ms
Size	2.36 MiB	2.91 MiB	558.22 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
80b2ce3+dirty	1265.92 ms	1268.60 ms	2.69 ms
d7401ac+dirty	1252.38 ms	1275.04 ms	22.66 ms
e5c9b8b+dirty	1258.57 ms	1267.32 ms	8.75 ms
acadc0f+dirty	1264.38 ms	1290.06 ms	25.68 ms
728164b+dirty	1256.10 ms	1259.08 ms	2.98 ms
3ffcddd+dirty	1244.47 ms	1264.14 ms	19.67 ms
9a3ca65+dirty	1247.06 ms	1274.58 ms	27.52 ms
457e29f+dirty	1253.94 ms	1269.18 ms	15.24 ms
12427f4+dirty	1267.15 ms	1271.30 ms	4.15 ms
2534337+dirty	1225.08 ms	1230.26 ms	5.17 ms

App size

Revision	Plain	With Sentry	Diff
80b2ce3+dirty	2.36 MiB	2.84 MiB	486.98 KiB
d7401ac+dirty	2.36 MiB	2.83 MiB	481.14 KiB
e5c9b8b+dirty	2.36 MiB	2.87 MiB	520.43 KiB
acadc0f+dirty	2.36 MiB	2.83 MiB	480.37 KiB
728164b+dirty	2.36 MiB	2.88 MiB	530.38 KiB
3ffcddd+dirty	2.36 MiB	2.84 MiB	489.60 KiB
9a3ca65+dirty	2.36 MiB	2.82 MiB	462.89 KiB
457e29f+dirty	2.36 MiB	2.87 MiB	520.67 KiB
12427f4+dirty	2.36 MiB	2.88 MiB	530.38 KiB
2534337+dirty	2.36 MiB	2.88 MiB	525.47 KiB

[lucas-zimerman]

lgtm!